Chapter 14 SQL Statement Syntax

It is intended when upgrading MySQL to 5.1 or later from older versions.

It is intended to update a database directory name to the current encoding format if the name contains special characters that need encoding.

The statement is used by mysqlcheck (as invoked by mysql_upgrade).

To use ALTER TABLE, you need ALTER, CREATE, and INSERT privileges for the table. Renaming a table requires ALTER and DROP on the old table, ALTER, CREATE, and INSERT on the new table.

Following the table name, specify the alterations to be made. If none are given, ALTER TABLE does nothing.

The syntax for many of the permissible alterations is similar to clauses of the CREATE TABLE statement. column_definition clauses use the same syntax for ADD and CHANGE as for CREATE TABLE. See Section 14.1.18, “CREATE TABLE Syntax”, for more information.

The word COLUMN is optional and can be omitted.

You can issue multiple ADD, ALTER, DROP, and CHANGE clauses in a single ALTER TABLE statement, separated by commas. This is a MySQL extension to standard SQL, which permits only one of each clause per ALTER TABLE statement. For example, to drop multiple columns in a single statement, do this:

ALTER TABLE t2 DROP COLUMN c, DROP COLUMN d;

Some operations may result in warnings if attempted on a table for which the storage engine does not support the operation. These warnings can be displayed with SHOW WARNINGS. See Section 14.7.5.40, “SHOW WARNINGS Syntax”. For information on troubleshooting ALTER TABLE, see Section B.5.6.1, “Problems with ALTER TABLE”.

For usage examples, see Section 14.1.8.4, “ALTER TABLE Examples”.

For information about generated columns, see Section 14.1.8.3, “ALTER TABLE and Generated Columns”.

With the mysql_info() C API function, you can find out how many rows were copied by ALTER TABLE. See Section 27.8.7.36, “mysql_info()”.

Table Options

Performance and Storage Considerations

Using the LOCK Clause to Control Concurrency

Column Attributes

Primary Keys and Indexes

Foreign Keys

Dropping Columns

Changing the Character Set

Discarding and Importing InnoDB Tablespaces

Row Order for MyISAM Tables

Partitioning Options

If t1 is currently not an InnoDB table, this statement changes its storage engine to InnoDB:

ALTER TABLE t1 ENGINE = InnoDB;

To change the InnoDB table to use compressed row-storage format:

ALTER TABLE t1 ROW_FORMAT = COMPRESSED;

If the InnoDB tablespace encryption feature is enabled (see Section 15.7.10, “InnoDB Tablespace Encryption”), encryption for t1 can be enabled or disabled like this:

ALTER TABLE t1 ENCRYPTION='Y';
ALTER TABLE t1 ENCRYPTION='N';

To reset the current auto-increment value:

ALTER TABLE t1 AUTO_INCREMENT = 13;

You cannot reset the counter to a value less than or equal to the value that is currently in use. For both InnoDB and MyISAM, if the value is less than or equal to the maximum value currently in the AUTO_INCREMENT column, the value is reset to the current maximum AUTO_INCREMENT column value plus one.

To change the default table character set:

ALTER TABLE t1 CHARACTER SET = utf8;

To add (or change) a table comment:

ALTER TABLE t1 COMMENT = 'New table comment';

You can use ALTER TABLE with the TABLESPACE option to move non-partitioned InnoDB tables between existing general tablespaces, file-per-table tablespaces, and the system tablespace. See Moving Non-Partitioned Tables Between Tablespaces Using ALTER TABLE.

MySQL NDB Cluster 7.5.2 and later supports setting NDB_TABLE options for controlling a table's partition balance (fragment count type), read-from-any-replica capability, full replication, or any combination of these, as part of the table comment for an ALTER TABLE statement in the same manner as for CREATE TABLE, as shown in this example:

ALTER TABLE t1 COMMENT = "NDB_TABLE=READ_BACKUP=0,PARTITION_BALANCE=FOR_RA_BY_NODE";

Bear in mind that ALTER TABLE ... COMMENT ... discards any existing comment for the table. See Setting NDB_TABLE options, for additional information and examples.

ALTER TABLE operations on InnoDB tables that are supported by the InnoDB online DDL feature. For an overview of supported operations, see Section 15.13.1, “Overview of Online DDL”. For information about performance and concurrency of online DDL operations, see Section 15.13.2, “Performance and Concurrency Considerations for Online DDL”.

ALTER TABLE tbl_name RENAME TO new_tbl_name. When run without other options, MySQL renames files that correspond to the table tbl_name without making a copy. (You can also use the RENAME TABLE statement to rename tables. See Section 14.1.33, “RENAME TABLE Syntax”.) Privileges granted specifically for the renamed table are not migrated to the new name. They must be changed manually.

Alterations that modify only table metadata and not table data are immediate because the server only needs to alter the table .frm file, not touch table contents. The following changes are made in this way:

Renaming an index.

Adding or dropping an index, for InnoDB and NDB. See Section 15.13.1, “Overview of Online DDL”.

For NDB tables, operations that add and drop indexes on variable-width columns occur online, without table copying and without blocking concurrent DML actions for most of their duration. See Section 14.1.8.2, “ALTER TABLE Online Operations in MySQL Cluster”.

LOCK = DEFAULT

Maximum level of concurrency for the given ALGORITHM clause (if any) and ALTER TABLE operation: Permit concurrent reads and writes if supported. If not, permit concurrent reads if supported. If not, enforce exclusive access.

LOCK = NONE

If supported, permit concurrent reads and writes. Otherwise, return an error message.

LOCK = SHARED

If supported, permit concurrent reads but block writes. Note that writes will be blocked even if concurrent writes are supported by the storage engine for the given ALGORITHM clause (if any) and ALTER TABLE operation. If concurrent reads are not supported, return an error message.

LOCK = EXCLUSIVE

Enforce exclusive access. This will be done even if concurrent reads/writes are supported by the storage engine for the given ALGORITHM clause (if any) and ALTER TABLE operation.

You can rename a column using a CHANGE old_col_name new_col_name column_definition clause. To do so, specify the old and new column names and the definition that the column currently has. For example, to rename an INTEGER column from a to b, you can do this:

ALTER TABLE t1 CHANGE a b INTEGER;

To change a column's type but not the name, CHANGE syntax still requires an old and new column name, even if they are the same. For example:

ALTER TABLE t1 CHANGE b b BIGINT NOT NULL;

You can also use MODIFY to change a column's type without renaming it:

ALTER TABLE t1 MODIFY b BIGINT NOT NULL;

MODIFY is an extension to ALTER TABLE for Oracle compatibility.

When you use CHANGE or MODIFY, column_definition must include the data type and all attributes that should apply to the new column, other than index attributes such as PRIMARY KEY or UNIQUE. Attributes present in the original definition but not specified for the new definition are not carried forward. Suppose that a column col1 is defined as INT UNSIGNED DEFAULT 1 COMMENT 'my column' and you modify the column as follows:

ALTER TABLE t1 MODIFY col1 BIGINT;

The resulting column will be defined as BIGINT, but will not include the attributes UNSIGNED DEFAULT 1 COMMENT 'my column'. To retain them, the statement should be:

ALTER TABLE t1 MODIFY col1 BIGINT UNSIGNED DEFAULT 1 COMMENT 'my column';

When you change a data type using CHANGE or MODIFY, MySQL tries to convert existing column values to the new type as well as possible.

To add a column at a specific position within a table row, use FIRST or AFTER col_name. The default is to add the column last. You can also use FIRST and AFTER in CHANGE or MODIFY operations to reorder columns within a table.

If you use CHANGE or MODIFY to shorten a column for which an index exists on the column, and the resulting column length is less than the index length, MySQL shortens the index automatically.

CHANGE col_name is a MySQL extension to standard SQL.

ALTER ... SET DEFAULT or ALTER ... DROP DEFAULT specify a new default value for a column or remove the old default value, respectively. If the old default is removed and the column can be NULL, the new default is NULL. If the column cannot be NULL, MySQL assigns a default value as described in Section 12.7, “Data Type Default Values”.

DROP PRIMARY KEY drops the primary key. If there is no primary key, an error occurs. For information about the performance characteristics of primary keys, especially for InnoDB tables, see Section 9.3.2, “Using Primary Keys”.

If you add a UNIQUE INDEX or PRIMARY KEY to a table, MySQL stores it before any nonunique index to permit detection of duplicate keys as early as possible.

DROP INDEX removes an index. This is a MySQL extension to standard SQL. See Section 14.1.25, “DROP INDEX Syntax”. If you are unsure of the index name, use SHOW INDEX FROM tbl_name.

Some storage engines permit you to specify an index type when creating an index. The syntax for the index_type specifier is USING type_name. For details about USING, see Section 14.1.14, “CREATE INDEX Syntax”. The preferred position is after the column list. Support for use of the option before the column list will be removed in a future MySQL release.

index_option values specify additional options for an index. For details about permissible index_option values, see Section 14.1.14, “CREATE INDEX Syntax”.

RENAME INDEX old_index_name TO new_index_name renames an index. This is a MySQL extension to standard SQL. The content of the table remains unchanged. old_index_name must be the name of an existing index in the table that is not dropped by the same ALTER TABLE statement. new_index_name is the new index name, which cannot duplicate the name of an index in the resulting table after changes have been applied. Neither index name can be PRIMARY.

If you use ALTER TABLE on a MyISAM table, all nonunique indexes are created in a separate batch (as for REPAIR TABLE). This should make ALTER TABLE much faster when you have many indexes.

For MyISAM tables, key updating can be controlled explicitly. Use ALTER TABLE ... DISABLE KEYS to tell MySQL to stop updating nonunique indexes. Then use ALTER TABLE ... ENABLE KEYS to re-create missing indexes. MyISAM does this with a special algorithm that is much faster than inserting keys one by one, so disabling keys before performing bulk insert operations should give a considerable speedup. Using ALTER TABLE ... DISABLE KEYS requires the INDEX privilege in addition to the privileges mentioned earlier.

While the nonunique indexes are disabled, they are ignored for statements such as SELECT and EXPLAIN that otherwise would use them.

After an ALTER TABLE statement, it may be necessary to run ANALYZE TABLE to update index cardinality information. See Section 14.7.5.22, “SHOW INDEX Syntax”.

The FOREIGN KEY and REFERENCES clauses are supported by the InnoDB and NDB storage engines, which implement ADD [CONSTRAINT [symbol]] FOREIGN KEY [index_name] (...) REFERENCES ... (...). See Section 1.8.3.2, “FOREIGN KEY Constraints”; for information sepcific to InnoDB, see Section 15.8.7, “InnoDB and FOREIGN KEY Constraints”.

For other storage engines, the clauses are parsed but ignored. The CHECK clause is parsed but ignored by all storage engines. See Section 14.1.18, “CREATE TABLE Syntax”. The reason for accepting but ignoring syntax clauses is for compatibility, to make it easier to port code from other SQL servers, and to run applications that create tables with references. See Section 1.8.2, “MySQL Differences from Standard SQL”.

For ALTER TABLE, unlike CREATE TABLE, ADD FOREIGN KEY ignores index_name if given and uses an automatically generated foreign key name. As a workaround, include the CONSTRAINT clause to specify the foreign key name:

ADD CONSTRAINT name FOREIGN KEY (....) ...

MySQL Server and MySQL Cluster both support the use of ALTER TABLE to drop foreign keys:

ALTER TABLE tbl_name DROP FOREIGN KEY fk_symbol;

Adding and dropping a foreign key in the same ALTER TABLE statement is supported for ALTER TABLE ... ALGORITHM=INPLACE but is unsupported for ALTER TABLE ... ALGORITHM=COPY.

The server prohibits changes to foreign key columns that have the potential to cause loss of referential integrity. It also prohibits changes to the data type of such columns that may be unsafe. For example, changing VARCHAR(20) to VARCHAR(30) is permitted, but changing it to VARCHAR(1024) is not because that alters the number of length bytes required to store individual values. A workaround is to use ALTER TABLE ... DROP FOREIGN KEY before changing the column definition and ALTER TABLE ... ADD FOREIGN KEY afterward.

ALTER TABLE tbl_name RENAME new_tbl_name changes internally generated foreign key constraint names and user-defined foreign key constraint names that contain the string “tbl_name_ibfk_” to reflect the new table name. InnoDB interprets foreign key constraint names that contain the string “tbl_name_ibfk_” as internally generated names.

If a table contains only one column, the column cannot be dropped. If what you intend is to remove the table, use DROP TABLE instead.

If columns are dropped from a table, the columns are also removed from any index of which they are a part. If all columns that make up an index are dropped, the index is dropped as well.

DROP col_name is a MySQL extension to standard SQL.

The keywords CREATE EVENT plus an event name, which uniquely identifies the event in a database schema.

An ON SCHEDULE clause, which determines when and how often the event executes.

A DO clause, which contains the SQL statement to be executed by an event.

If you do not have the SUPER privilege, the only permitted user value is your own account, either specified literally or by using CURRENT_USER. You cannot set the definer to some other account.

If you have the SUPER privilege, you can specify any syntactically valid account name. If the account does not exist, a warning is generated.

Although it is possible to create an event with a nonexistent DEFINER account, an error occurs at event execution time if the account does not exist.

AT timestamp is used for a one-time event. It specifies that the event executes one time only at the date and time given by timestamp, which must include both the date and time, or must be an expression that resolves to a datetime value. You may use a value of either the DATETIME or TIMESTAMP type for this purpose. If the date is in the past, a warning occurs, as shown here:

mysql> SELECT NOW();
+---------------------+
| NOW()               |
+---------------------+
| 2006-02-10 23:59:01 |
+---------------------+
1 row in set (0.04 sec)

mysql> CREATE EVENT e_totals
    ->     ON SCHEDULE AT '2006-02-10 23:59:00'
    ->     DO INSERT INTO test.totals VALUES (NOW());
Query OK, 0 rows affected, 1 warning (0.00 sec)

mysql> SHOW WARNINGS\G
*************************** 1. row ***************************
  Level: Note
   Code: 1588
Message: Event execution time is in the past and ON COMPLETION NOT
         PRESERVE is set. The event was dropped immediately after
         creation.

CREATE EVENT statements which are themselves invalid—for whatever reason—fail with an error.

You may use CURRENT_TIMESTAMP to specify the current date and time. In such a case, the event acts as soon as it is created.

To create an event which occurs at some point in the future relative to the current date and time—such as that expressed by the phrase “three weeks from now”—you can use the optional clause + INTERVAL interval. The interval portion consists of two parts, a quantity and a unit of time, and follows the same syntax rules that govern intervals used in the DATE_ADD() function (see Section 13.7, “Date and Time Functions”. The units keywords are also the same, except that you cannot use any units involving microseconds when defining an event. With some interval types, complex time units may be used. For example, “two minutes and ten seconds” can be expressed as + INTERVAL '2:10' MINUTE_SECOND.

You can also combine intervals. For example, AT CURRENT_TIMESTAMP + INTERVAL 3 WEEK + INTERVAL 2 DAY is equivalent to “three weeks and two days from now”. Each portion of such a clause must begin with + INTERVAL.

To repeat actions at a regular interval, use an EVERY clause. The EVERY keyword is followed by an interval as described in the previous discussion of the AT keyword. (+ INTERVAL is not used with EVERY.) For example, EVERY 6 WEEK means “every six weeks”.

Although + INTERVAL clauses are not permitted in an EVERY clause, you can use the same complex time units permitted in a + INTERVAL.

An EVERY clause may contain an optional STARTS clause. STARTS is followed by a timestamp value that indicates when the action should begin repeating, and may also use + INTERVAL interval to specify an amount of time “from now”. For example, EVERY 3 MONTH STARTS CURRENT_TIMESTAMP + INTERVAL 1 WEEK means “every three months, beginning one week from now”. Similarly, you can express “every two weeks, beginning six hours and fifteen minutes from now” as EVERY 2 WEEK STARTS CURRENT_TIMESTAMP + INTERVAL '6:15' HOUR_MINUTE. Not specifying STARTS is the same as using STARTS CURRENT_TIMESTAMP—that is, the action specified for the event begins repeating immediately upon creation of the event.

An EVERY clause may contain an optional ENDS clause. The ENDS keyword is followed by a timestamp value that tells MySQL when the event should stop repeating. You may also use + INTERVAL interval with ENDS; for instance, EVERY 12 HOUR STARTS CURRENT_TIMESTAMP + INTERVAL 30 MINUTE ENDS CURRENT_TIMESTAMP + INTERVAL 4 WEEK is equivalent to “every twelve hours, beginning thirty minutes from now, and ending four weeks from now”. Not using ENDS means that the event continues executing indefinitely.

ENDS supports the same syntax for complex time units as STARTS does.

You may use STARTS, ENDS, both, or neither in an EVERY clause.

If a repeating event does not terminate within its scheduling interval, the result may be multiple instances of the event executing simultaneously. If this is undesirable, you should institute a mechanism to prevent simultaneous instances. For example, you could use the GET_LOCK() function, or row or table locking.

For information about creating stored functions, see Section 14.1.16, “CREATE PROCEDURE and CREATE FUNCTION Syntax”.

For information about creating user-defined functions, see Section 14.7.3.1, “CREATE FUNCTION Syntax for User-Defined Functions”.

Prefixes can be specified for CHAR, VARCHAR, BINARY, and VARBINARY column indexes.

Prefixes must be specified for BLOB and TEXT column indexes.

Prefix limits are measured in bytes, whereas the prefix length in CREATE TABLE, ALTER TABLE, and CREATE INDEX statements is interpreted as number of characters for nonbinary string types (CHAR, VARCHAR, TEXT) and number of bytes for binary string types (BINARY, VARBINARY, BLOB). Take this into account when specifying a prefix length for a nonbinary string column that uses a multibyte character set.

For spatial columns, prefix values cannot be given, as described later in this section.

Available only for MyISAM and InnoDB tables. Specifying SPATIAL INDEX for other storage engines results in an error.

Indexed columns must be NOT NULL.

Column prefix lengths are prohibited. The full width of each column is indexed.

Permitted for any storage engine that supports spatial columns except ARCHIVE.

Columns can be NULL unless the index is a primary key.

For each spatial column in a non-SPATIAL index except POINT columns, a column prefix length must be specified. (This is the same requirement as for indexed BLOB columns.) The prefix length is given in bytes.

The index type for a non-SPATIAL index depends on the storage engine. Currently, B-tree is used.

You can add an index on a column that can have NULL values only for InnoDB, MyISAM, and MEMORY tables.

You can add an index on a BLOB or TEXT column only for using the InnoDB and MyISAM tables.

When the innodb_stats_persistent setting is enabled, run the ANALYZE TABLE statement for an InnoDB table after creating an index on that table.

KEY_BLOCK_SIZE [=] value

For MyISAM tables, KEY_BLOCK_SIZE optionally specifies the size in bytes to use for index key blocks. The value is treated as a hint; a different size could be used if necessary. A KEY_BLOCK_SIZE value specified for an individual index definition overrides a table-level KEY_BLOCK_SIZE value.

KEY_BLOCK_SIZE is not supported at the index level for InnoDB tables. See Section 14.1.18, “CREATE TABLE Syntax”.

index_type

Some storage engines permit you to specify an index type when creating an index. For example:

CREATE TABLE lookup (id INT) ENGINE = MEMORY;
CREATE INDEX id_index ON lookup (id) USING BTREE;

Table 14.1, “Index Types Per Storage Engine” shows the permissible index type values supported by different storage engines. Where multiple index types are listed, the first one is the default when no index type specifier is given. Storage engines not listed in the table do not support an index_type clause in index definitions.

The index_type clause cannot be used for FULLTEXT INDEX or SPATIAL INDEX specifications. Full-text index implementation is storage engine dependent. Spatial indexes are implemented as R-tree indexes.

BTREE indexes are implemented by the NDB storage engine as T-tree indexes.

If you specify an index type that is not valid for a given storage engine, but another index type is available that the engine can use without affecting query results, the engine uses the available type. The parser recognizes RTREE as a type name, but currently this cannot be specified for any storage engine.

TYPE type_name is recognized as a synonym for USING type_name. However, USING is the preferred form.

For the storage engines that support an index_type option, Table 14.2, “Storage Engine Index Characteristics” shows some characteristics of index use.

Table note:

1. If USING HASH is specified that prevents creation of an implicit ordered index.

WITH PARSER parser_name

This option can be used only with FULLTEXT indexes. It associates a parser plugin with the index if full-text indexing and searching operations need special handling. InnoDB and MyISAM support full-text parser plugins. See Full-Text Parser Plugins and Section 28.2.4.4, “Writing Full-Text Parser Plugins” for more information.

COMMENT 'string'

Index definitions can include an optional comment of up to 1024 characters.

The MERGE_THRESHOLD for index pages can be configured for individual indexes using the index_option COMMENT clause of the CREATE INDEX statement. For example:

CREATE TABLE t1 (id INT);
CREATE INDEX id_index ON t1 (id) COMMENT 'MERGE_THRESHOLD=40';

If the page-full percentage for an index page falls below the MERGE_THRESHOLD value when a row is deleted or when a row is shortened by an update operation, InnoDB attempts to merge the index page with a neighboring index page. The default MERGE_THRESHOLD value is 50, which is the previously hardcoded value.

MERGE_THRESHOLD can also be defined at the index level and table level using CREATE TABLE and ALTER TABLE statements. For more information, see Section 15.6.13, “Configuring the Merge Threshold for Index Pages”.

CONTAINS SQL indicates that the routine does not contain statements that read or write data. This is the default if none of these characteristics is given explicitly. Examples of such statements are SET @x = 1 or DO RELEASE_LOCK('abc'), which execute but neither read nor write data.

NO SQL indicates that the routine contains no SQL statements.

READS SQL DATA indicates that the routine contains statements that read data (for example, SELECT), but not statements that write data.

MODIFIES SQL DATA indicates that the routine contains statements that may write data (for example, INSERT or DELETE).

If you do not have the SUPER privilege, the only permitted user value is your own account, either specified literally or by using CURRENT_USER. You cannot set the definer to some other account.

If you have the SUPER privilege, you can specify any syntactically valid account name. If the account does not exist, a warning is generated.

Although it is possible to create a routine with a nonexistent DEFINER account, an error occurs at routine execution time if the SQL SECURITY value is DEFINER but the definer account does not exist.

Assignments are checked for data type mismatches and overflow. Conversion and overflow problems result in warnings, or errors in strict SQL mode.

Only scalar values can be assigned. For example, a statement such as SET x = (SELECT 1, 2) is invalid.

For character data types, if there is a CHARACTER SET attribute in the declaration, the specified character set and its default collation is used. If the COLLATE attribute is also present, that collation is used rather than the default collation.

If CHARACTER SET and COLLATE attributes are not present, the database character set and collation in effect at routine creation time are used. To avoid having the server use the database character set and collation, provide explicit CHARACTER SET and COLLATE attributes for character data parameters.

If you change the database default character set or collation, stored routines that use the database defaults must be dropped and recreated so that they use the new defaults.

The database character set and collation are given by the value of the character_set_database and collation_database system variables. For more information, see Section 11.1.3.3, “Database Character Set and Collation”.

Temporary Tables

Table Name

Cloning or Copying a Table

Column Data Types and Attributes

Indexes and Foreign Keys

Table Options

Creating Partitioned Tables

tbl_name

The table name can be specified as db_name.tbl_name to create the table in a specific database. This works regardless of whether there is a default database, assuming that the database exists. If you use quoted identifiers, quote the database and table names separately. For example, write `mydb`.`mytbl`, not `mydb.mytbl`.

Rules for permissible table names are given in Section 10.2, “Schema Object Names”.

IF NOT EXISTS

Prevents an error from occurring if the table exists. However, there is no verification that the existing table has a structure identical to that indicated by the CREATE TABLE statement.

LIKE

Use CREATE TABLE ... LIKE to create an empty table based on the definition of another table, including any column attributes and indexes defined in the original table:

CREATE TABLE new_tbl LIKE orig_tbl;

For more information, see Section 14.1.18.3, “CREATE TABLE ... LIKE Syntax”.

[AS] query_expression

To create one table from another, add a SELECT statement at the end of the CREATE TABLE statement:

CREATE TABLE new_tbl AS SELECT * FROM orig_tbl;

For more information, see Section 14.1.18.4, “CREATE TABLE ... SELECT Syntax”.

IGNORE|REPLACE

The IGNORE and REPLACE options indicate how to handle rows that duplicate unique key values when copying a table using a SELECT statement.

For more information, see Section 14.1.18.4, “CREATE TABLE ... SELECT Syntax”.

data_type

data_type represents the data type in a column definition. spatial_type represents a spatial data type. The data type syntax shown is representative only. For a full description of the syntax available for specifying column data types, as well as information about the properties of each type, see Chapter 12, Data Types, and Section 12.5, “Extensions for Spatial Data”. Beginning with MySQL 5.7.8, a JSON data type is also supported for table columns; see Section 12.6, “The JSON Data Type”, for more information.

NOT NULL | NULL

If neither NULL nor NOT NULL is specified, the column is treated as though NULL had been specified.

In MySQL 5.7, only the InnoDB, MyISAM, and MEMORY storage engines support indexes on columns that can have NULL values. In other cases, you must declare indexed columns as NOT NULL or an error results.

DEFAULT

Specifies a default value for a column. With one exception, the default value must be a constant; it cannot be a function or an expression. This means, for example, that you cannot set the default for a date column to be the value of a function such as NOW() or CURRENT_DATE. The exception is that you can specify CURRENT_TIMESTAMP as the default for a TIMESTAMP or DATETIME column. See Section 12.3.5, “Automatic Initialization and Updating for TIMESTAMP and DATETIME”.

If a column definition includes no explicit DEFAULT value, MySQL determines the default value as described in Section 12.7, “Data Type Default Values”.

BLOB, TEXT, and JSON columns cannot be assigned a default value.

If the NO_ZERO_DATE or NO_ZERO_IN_DATE SQL mode is enabled and a date-valued default is not correct according to that mode, CREATE TABLE produces a warning if strict SQL mode is not enabled and an error if strict mode is enabled. For example, with NO_ZERO_IN_DATE enabled, c1 DATE DEFAULT '2010-00-00' produces a warning.

AUTO_INCREMENT

An integer or floating-point column can have the additional attribute AUTO_INCREMENT. When you insert a value of NULL (recommended) or 0 into an indexed AUTO_INCREMENT column, the column is set to the next sequence value. Typically this is value+1, where value is the largest value for the column currently in the table. AUTO_INCREMENT sequences begin with 1.

To retrieve an AUTO_INCREMENT value after inserting a row, use the LAST_INSERT_ID() SQL function or the mysql_insert_id() C API function. See Section 13.14, “Information Functions”, and Section 27.8.7.38, “mysql_insert_id()”.

If the NO_AUTO_VALUE_ON_ZERO SQL mode is enabled, you can store 0 in AUTO_INCREMENT columns as 0 without generating a new sequence value. See Section 6.1.8, “Server SQL Modes”.

There can be only one AUTO_INCREMENT column per table, it must be indexed, and it cannot have a DEFAULT value. An AUTO_INCREMENT column works properly only if it contains only positive values. Inserting a negative number is regarded as inserting a very large positive number. This is done to avoid precision problems when numbers “wrap” over from positive to negative and also to ensure that you do not accidentally get an AUTO_INCREMENT column that contains 0.

For MyISAM tables, you can specify an AUTO_INCREMENT secondary column in a multiple-column key. See Section 4.6.9, “Using AUTO_INCREMENT”.

To make MySQL compatible with some ODBC applications, you can find the AUTO_INCREMENT value for the last inserted row with the following query:

SELECT * FROM tbl_name WHERE auto_col IS NULL

This method requires that sql_auto_is_null variable is not set to 0. See Section 6.1.5, “Server System Variables”.

For information about InnoDB and AUTO_INCREMENT, see Section 15.8.6, “AUTO_INCREMENT Handling in InnoDB”. For information about AUTO_INCREMENT and MySQL Replication, see Section 18.4.1.1, “Replication and AUTO_INCREMENT”.

COMMENT

A comment for a column can be specified with the COMMENT option, up to 1024 characters long. The comment is displayed by the SHOW CREATE TABLE and SHOW FULL COLUMNS statements.

COLUMN_FORMAT

In MySQL Cluster, it is also possible to specify a data storage format for individual columns of NDB tables using COLUMN_FORMAT. Permissible column formats are FIXED, DYNAMIC, and DEFAULT. FIXED is used to specify fixed-width storage, DYNAMIC permits the column to be variable-width, and DEFAULT causes the column to use fixed-width or variable-width storage as determined by the column's data type (possibly overridden by a ROW_FORMAT specifier).

Beginning with MySQL NDB Cluster 7.5.4, for NDB tables, the default value for COLUMN_FORMAT is FIXED. (The default had been switched to DYNAMIC in MySQL NDB Cluster 7.5.1, but this change was reverted to maintain backwards compatibility with existing GA release series.) (Bug #24487363)

COLUMN_FORMAT currently has no effect on columns of tables using storage engines other than NDB. In MySQL 5.7 and later, COLUMN_FORMAT is silently ignored.

STORAGE

For NDB tables, it is possible to specify whether the column is stored on disk or in memory by using a STORAGE clause. STORAGE DISK causes the column to be stored on disk, and STORAGE MEMORY causes in-memory storage to be used. The CREATE TABLE statement used must still include a TABLESPACE clause:

mysql> CREATE TABLE t1 (
    ->     c1 INT STORAGE DISK,
    ->     c2 INT STORAGE MEMORY
    -> ) ENGINE NDB;
ERROR 1005 (HY000): Can't create table 'c.t1' (errno: 140)

mysql> CREATE TABLE t1 (
    ->     c1 INT STORAGE DISK,
    ->     c2 INT STORAGE MEMORY
    -> ) TABLESPACE ts_1 ENGINE NDB;
Query OK, 0 rows affected (1.06 sec)

For NDB tables, STORAGE DEFAULT is equivalent to STORAGE MEMORY.

The STORAGE clause has no effect on tables using storage engines other than NDB. The STORAGE keyword is supported only in the build of mysqld that is supplied with MySQL Cluster; it is not recognized in any other version of MySQL, where any attempt to use the STORAGE keyword causes a syntax error.

GENERATED ALWAYS

Used to specify a generated column expression. For information about generated columns, see Section 14.1.18.7, “CREATE TABLE and Generated Columns”.

Generated stored columns can be indexed. InnoDB supports secondary indexes on generated virtual columns. See Section 14.1.18.8, “Secondary Indexes and Generated Columns”.

CONSTRAINT symbol

If the CONSTRAINT symbol clause is given, the symbol value, if used, must be unique in the database. A duplicate symbol results in an error. If the clause is not given, or a symbol is not included following the CONSTRAINT keyword, a name for the constraint is created automatically.

PRIMARY KEY

A unique index where all key columns must be defined as NOT NULL. If they are not explicitly declared as NOT NULL, MySQL declares them so implicitly (and silently). A table can have only one PRIMARY KEY. The name of a PRIMARY KEY is always PRIMARY, which thus cannot be used as the name for any other kind of index.

If you do not have a PRIMARY KEY and an application asks for the PRIMARY KEY in your tables, MySQL returns the first UNIQUE index that has no NULL columns as the PRIMARY KEY.

In InnoDB tables, keep the PRIMARY KEY short to minimize storage overhead for secondary indexes. Each secondary index entry contains a copy of the primary key columns for the corresponding row. (See Section 15.8.9, “Clustered and Secondary Indexes”.)

In the created table, a PRIMARY KEY is placed first, followed by all UNIQUE indexes, and then the nonunique indexes. This helps the MySQL optimizer to prioritize which index to use and also more quickly to detect duplicated UNIQUE keys.

A PRIMARY KEY can be a multiple-column index. However, you cannot create a multiple-column index using the PRIMARY KEY key attribute in a column specification. Doing so only marks that single column as primary. You must use a separate PRIMARY KEY(index_col_name, ...) clause.

If a PRIMARY KEY consists of only one column that has an integer type, you can also refer to the column as _rowid in SELECT statements.

In MySQL, the name of a PRIMARY KEY is PRIMARY. For other indexes, if you do not assign a name, the index is assigned the same name as the first indexed column, with an optional suffix (_2, _3, ...) to make it unique. You can see index names for a table using SHOW INDEX FROM tbl_name. See Section 14.7.5.22, “SHOW INDEX Syntax”.

KEY | INDEX

KEY is normally a synonym for INDEX. The key attribute PRIMARY KEY can also be specified as just KEY when given in a column definition. This was implemented for compatibility with other database systems.

UNIQUE

A UNIQUE index creates a constraint such that all values in the index must be distinct. An error occurs if you try to add a new row with a key value that matches an existing row. For all engines, a UNIQUE index permits multiple NULL values for columns that can contain NULL.

If a UNIQUE index consists of only one column that has an integer type, you can also refer to the column as _rowid in SELECT statements.

FULLTEXT

A FULLTEXT index is a special type of index used for full-text searches. Only the InnoDB and MyISAM storage engines support FULLTEXT indexes. They can be created only from CHAR, VARCHAR, and TEXT columns. Indexing always happens over the entire column; column prefix indexing is not supported and any prefix length is ignored if specified. See Section 13.9, “Full-Text Search Functions”, for details of operation. A WITH PARSER clause can be specified as an index_option value to associate a parser plugin with the index if full-text indexing and searching operations need special handling. This clause is valid only for FULLTEXT indexes. Both InnoDB and MyISAM support full-text parser plugins. See Full-Text Parser Plugins and Section 28.2.4.4, “Writing Full-Text Parser Plugins” for more information.

SPATIAL

You can create SPATIAL indexes on spatial data types. Spatial types are supported only for MyISAM and InnoDB tables, and indexed columns must be declared as NOT NULL. See Section 12.5, “Extensions for Spatial Data”.

FOREIGN KEY

MySQL supports foreign keys, which let you cross-reference related data across tables, and foreign key constraints, which help keep this spread-out data consistent. For definition and option information, see reference_definition, and reference_option.

Partitioned tables employing the InnoDB storage engine do not support foreign keys. See Section 22.6, “Restrictions and Limitations on Partitioning”, for more information.

CHECK

The CHECK clause is parsed but ignored by all storage engines. See Section 1.8.2.3, “Foreign Key Differences”.

index_col_name

index_type

Some storage engines permit you to specify an index type when creating an index. The syntax for the index_type specifier is USING type_name.

Example:

CREATE TABLE lookup
  (id INT, INDEX USING BTREE (id))
  ENGINE = MEMORY;

The preferred position for USING is after the index column list. It can be given before the column list, but support for use of the option in that position is deprecated and will be removed in a future MySQL release.

index_option

index_option values specify additional options for an index.

For more information about permissible index_option values, see Section 14.1.14, “CREATE INDEX Syntax”. For more information about indexes, see Section 9.3.1, “How MySQL Uses Indexes”.

reference_definition

For reference_definition syntax details and examples, see Section 14.1.18.5, “Using FOREIGN KEY Constraints”. For information specific to foreign keys in InnoDB, see Section 15.8.7, “InnoDB and FOREIGN KEY Constraints”.

InnoDB and NDB tables support checking of foreign key constraints. The columns of the referenced table must always be explicitly named. Both ON DELETE and ON UPDATE actions on foreign keys are supported. For more detailed information and examples, see Section 14.1.18.5, “Using FOREIGN KEY Constraints”. For information specific to foreign keys in InnoDB, see Section 15.8.7, “InnoDB and FOREIGN KEY Constraints”.

For other storage engines, MySQL Server parses and ignores the FOREIGN KEY and REFERENCES syntax in CREATE TABLE statements. See Section 1.8.2.3, “Foreign Key Differences”.

reference_option

For information about the RESTRICT, CASCADE, SET NULL, NO ACTION, and SET DEFAULT options, see Section 14.1.18.5, “Using FOREIGN KEY Constraints”.

ENGINE

Specifies the storage engine for the table, using one of the names shown in the following table. The engine name can be unquoted or quoted. The quoted name 'DEFAULT' is recognized but ignored.

By default, if a storage engine is specified that is not available, the statement fails with an error. You can override this behavior by removing NO_ENGINE_SUBSTITUTION from the server SQL mode (see Section 6.1.8, “Server SQL Modes”) so that MySQL allows substitution of the specified engine with the default storage engine instead. Normally in such cases, this is InnoDB, which is the default value for the default_storage_engine system variable. When NO_ENGINE_SUBSTITUTION is disabled, a warning occurs if the storage engine specification is not honored.

AUTO_INCREMENT

The initial AUTO_INCREMENT value for the table. In MySQL 5.7, this works for MyISAM, MEMORY, InnoDB, and ARCHIVE tables. To set the first auto-increment value for engines that do not support the AUTO_INCREMENT table option, insert a “dummy” row with a value one less than the desired value after creating the table, and then delete the dummy row.

For engines that support the AUTO_INCREMENT table option in CREATE TABLE statements, you can also use ALTER TABLE tbl_name AUTO_INCREMENT = N to reset the AUTO_INCREMENT value. The value cannot be set lower than the maximum value currently in the column.

AVG_ROW_LENGTH

An approximation of the average row length for your table. You need to set this only for large tables with variable-size rows.

When you create a MyISAM table, MySQL uses the product of the MAX_ROWS and AVG_ROW_LENGTH options to decide how big the resulting table is. If you don't specify either option, the maximum size for MyISAM data and index files is 256TB by default. (If your operating system does not support files that large, table sizes are constrained by the file size limit.) If you want to keep down the pointer sizes to make the index smaller and faster and you don't really need big files, you can decrease the default pointer size by setting the myisam_data_pointer_size system variable. (See Section 6.1.5, “Server System Variables”.) If you want all your tables to be able to grow above the default limit and are willing to have your tables slightly slower and larger than necessary, you can increase the default pointer size by setting this variable. Setting the value to 7 permits table sizes up to 65,536TB.

[DEFAULT] CHARACTER SET

Specifies a default character set for the table. CHARSET is a synonym for CHARACTER SET. If the character set name is DEFAULT, the database character set is used.

CHECKSUM

Set this to 1 if you want MySQL to maintain a live checksum for all rows (that is, a checksum that MySQL updates automatically as the table changes). This makes the table a little slower to update, but also makes it easier to find corrupted tables. The CHECKSUM TABLE statement reports the checksum. (MyISAM only.)

[DEFAULT] COLLATE

Specifies a default collation for the table.

COMMENT

A comment for the table, up to 2048 characters long.

You can set the InnoDB MERGE_THRESHOLD value for a table using the table_option COMMENT clause. See Section 15.6.13, “Configuring the Merge Threshold for Index Pages”.

Setting NDB_TABLE options.  In MySQL NDB Cluster 7.5.2 and later, the table comment in a CREATE TABLE or ALTER TABLE statement can also be used to specify one to four of the NDB_TABLE options NOLOGGING, READ_BACKUP, PARTITION_BALANCE, or FULLY_REPLICATED as a set of name-value pairs, separated by commas if need be, immediately following the string NDB_TABLE= that begins the quoted comment text. An example statement using this syntax is shown here (emphasized text):

CREATE TABLE t1 (
    c1 INT NOT NULL AUTO_INCREMENT PRIMARY KEY,
    c2 VARCHAR(100),
    c3 VARCHAR(100) )
ENGINE=NDB
COMMENT="NDB_TABLE=READ_BACKUP=0,PARTITION_BALANCE=FOR_RP_BY_NODE";

Spaces are not permitted within the quoted string. The string is case-insensitive.

The comment is displayed as part of the ouput of SHOW CREATE TABLE. The text of the comment is also available as the TABLE_COMMENT column of the MySQL Information Schema TABLES table.

This comment syntax is also supported with ALTER TABLE statements for NDB tables. Keep in mind that a table comment used with ALTER TABLE replaces any existing comment which the table might have had perviously.

Setting the MERGE_THRESHOLD option in table comments is not supported for NDB tables (it is ignored).

For complete syntax information and examples, see Section 14.1.18.9, “Setting NDB_TABLE Options in Table Comments”.

COMPRESSION

The compression algorithm used for page level compression for InnoDB tables. Supported values include Zlib, LZ4, and None. The COMPRESSION attribute was introduced with the transparent page compression feature. Page compression is only supported with InnoDB tables that reside in file-per-table tablespaces, and is only available on Linux and Windows platforms that support sparse files and hole punching. For more information, see Section 15.9.2, “InnoDB Page Compression”.

CONNECTION

The connection string for a FEDERATED table.

DATA DIRECTORY, INDEX DIRECTORY

For InnoDB, the DATA DIRECTORY='directory' option allows you to create InnoDB file-per-table tablespaces outside the MySQL data directory. Within the directory that you specify, MySQL creates a subdirectory corresponding to the database name, and within that a .ibd file for the table. The innodb_file_per_table configuration option must be enabled to use the DATA DIRECTORY option with InnoDB. The full directory path must be specified. See Section 15.7.5, “Creating a File-Per-Table Tablespace Outside the Data Directory” for more information.

When creating MyISAM tables, you can use the DATA DIRECTORY='directory' clause, the INDEX DIRECTORY='directory' clause, or both. They specify where to put a MyISAM table's data file and index file, respectively. Unlike InnoDB tables, MySQL does not create subdirectories that correspond to the database name when creating a MyISAM table with a DATA DIRECTORY or INDEX DIRECTORY option. Files are created in the directory that is specified.

As of MySQL 5.7.17, you must have the FILE privilege to use the DATA DIRECTORY or INDEX DIRECTORY table option.

These options work only when you are not using the --skip-symbolic-links option. Your operating system must also have a working, thread-safe realpath() call. See Section 9.12.3.2, “Using Symbolic Links for MyISAM Tables on Unix”, for more complete information.

If a MyISAM table is created with no DATA DIRECTORY option, the .MYD file is created in the database directory. By default, if MyISAM finds an existing .MYD file in this case, it overwrites it. The same applies to .MYI files for tables created with no INDEX DIRECTORY option. To suppress this behavior, start the server with the --keep_files_on_create option, in which case MyISAM will not overwrite existing files and returns an error instead.

If a MyISAM table is created with a DATA DIRECTORY or INDEX DIRECTORY option and an existing .MYD or .MYI file is found, MyISAM always returns an error. It will not overwrite a file in the specified directory.

DELAY_KEY_WRITE

Set this to 1 if you want to delay key updates for the table until the table is closed. See the description of the delay_key_write system variable in Section 6.1.5, “Server System Variables”. (MyISAM only.)

ENCRYPTION

Set the ENCRYPTION option to 'Y' to enable page-level data encryption for an InnoDB table created in a file-per-table tablespace. Option values are not case sensitive. The ENCRYPTION option was introduced with the InnoDB tablespace encryption feature; see Section 15.7.10, “InnoDB Tablespace Encryption”. The keyring_file plugin must be loaded to use the ENCRYPTION option.

INSERT_METHOD

If you want to insert data into a MERGE table, you must specify with INSERT_METHOD the table into which the row should be inserted. INSERT_METHOD is an option useful for MERGE tables only. Use a value of FIRST or LAST to have inserts go to the first or last table, or a value of NO to prevent inserts. See Section 16.7, “The MERGE Storage Engine”.

KEY_BLOCK_SIZE

For MyISAM tables, KEY_BLOCK_SIZE optionally specifies the size in bytes to use for index key blocks. The value is treated as a hint; a different size could be used if necessary. A KEY_BLOCK_SIZE value specified for an individual index definition overrides the table-level KEY_BLOCK_SIZE value.

For InnoDB tables, KEY_BLOCK_SIZE optionally specifies the page size (in kilobytes) to use for compressed InnoDB tables. The KEY_BLOCK_SIZE value is treated as a hint; a different size could be used by InnoDB if necessary. KEY_BLOCK_SIZE can only be less than or equal to the innodb_page_size value. A value of 0 represents the default compressed page size, which is half of the innodb_page_size value. Depending on innodb_page_size, possible KEY_BLOCK_SIZE values include 0, 1, 2, 4, 8, and 16. See Section 15.9.1, “InnoDB Table Compression” for more information.

Oracle recommends enabling innodb_strict_mode when specifying KEY_BLOCK_SIZE for InnoDB tables. When innodb_strict_mode is enabled, specifying an invalid KEY_BLOCK_SIZE value returns an error. If innodb_strict_mode is disabled, an invalid KEY_BLOCK_SIZE value results in a warning, and the KEY_BLOCK_SIZE option is ignored.

InnoDB only supports KEY_BLOCK_SIZE at the table level.

KEY_BLOCK_SIZE is not supported with 32k and 64k innodb_page_size values. InnoDB table compression does not support these pages sizes.

MAX_ROWS

The maximum number of rows you plan to store in the table. This is not a hard limit, but rather a hint to the storage engine that the table must be able to store at least this many rows.

The NDB storage engine treats this value as a maximum. If you plan to create very large MySQL Cluster tables (containing millions of rows), you should use this option to insure that NDB allocates sufficient number of index slots in the hash table used for storing hashes of the table's primary keys by setting MAX_ROWS = 2 * rows, where rows is the number of rows that you expect to insert into the table.

The maximum MAX_ROWS value is 4294967295; larger values are truncated to this limit.

MIN_ROWS

The minimum number of rows you plan to store in the table. The MEMORY storage engine uses this option as a hint about memory use.

PACK_KEYS

Takes effect only with MyISAM tables. Set this option to 1 if you want to have smaller indexes. This usually makes updates slower and reads faster. Setting the option to 0 disables all packing of keys. Setting it to DEFAULT tells the storage engine to pack only long CHAR, VARCHAR, BINARY, or VARBINARY columns.

If you do not use PACK_KEYS, the default is to pack strings, but not numbers. If you use PACK_KEYS=1, numbers are packed as well.

When packing binary number keys, MySQL uses prefix compression:

This means that if you have many equal keys on two consecutive rows, all following “same” keys usually only take two bytes (including the pointer to the row). Compare this to the ordinary case where the following keys takes storage_size_for_key + pointer_size (where the pointer size is usually 4). Conversely, you get a significant benefit from prefix compression only if you have many numbers that are the same. If all keys are totally different, you use one byte more per key, if the key is not a key that can have NULL values. (In this case, the packed key length is stored in the same byte that is used to mark if a key is NULL.)

PASSWORD

This option is unused. If you have a need to scramble your .frm files and make them unusable to any other MySQL server, please contact our sales department.

ROW_FORMAT

Defines the physical format in which the rows are stored.

When executing a CREATE TABLE statement, if you specify a row format that is not supported by the storage engine that is used for the table, the table is created using that storage engine's default row format. The information reported in this column in response to SHOW TABLE STATUS is the actual row format used. This may differ from the value in the Create_options column because the original CREATE TABLE definition is retained during creation.

Row format choices differ depending on the storage engine used for the table.

For InnoDB tables:

For MyISAM tables, the option value can be FIXED or DYNAMIC for static or variable-length row format. myisampack sets the type to COMPRESSED. See Section 16.2.3, “MyISAM Table Storage Formats”.

For NDB tables, the default ROW_FORMAT in MySQL NDB Cluster 7.5.1 and later is DYNAMIC. (Previously, it was FIXED.)

STATS_AUTO_RECALC

Specifies whether to automatically recalculate persistent statistics for an InnoDB table. The value DEFAULT causes the persistent statistics setting for the table to be determined by the innodb_stats_auto_recalc configuration option. The value 1 causes statistics to be recalculated when 10% of the data in the table has changed. The value 0 prevents automatic recalculation for this table; with this setting, issue an ANALYZE TABLE statement to recalculate the statistics after making substantial changes to the table. For more information about the persistent statistics feature, see Section 15.6.12.1, “Configuring Persistent Optimizer Statistics Parameters”.

STATS_PERSISTENT

Specifies whether to enable persistent statistics for an InnoDB table. The value DEFAULT causes the persistent statistics setting for the table to be determined by the innodb_stats_persistent configuration option. The value 1 enables persistent statistics for the table, while the value 0 turns off this feature. After enabling persistent statistics through a CREATE TABLE or ALTER TABLE statement, issue an ANALYZE TABLE statement to calculate the statistics, after loading representative data into the table. For more information about the persistent statistics feature, see Section 15.6.12.1, “Configuring Persistent Optimizer Statistics Parameters”.

STATS_SAMPLE_PAGES

The number of index pages to sample when estimating cardinality and other statistics for an indexed column, such as those calculated by ANALYZE TABLE. For more information, see Section 15.6.12.1, “Configuring Persistent Optimizer Statistics Parameters”.

TABLESPACE

The TABLESPACE option is used to create a table in an InnoDB general tablespace.

CREATE TABLE tbl_name ... TABLESPACE [=] tablespace_name

The general tablespace that you specify must exist prior to using the TABLESPACE option. For information about general tablespaces, see Section 15.7.9, “InnoDB General Tablespaces”.

The tablespace_name is a case-sensitive identifier. It may be quoted or unquoted. The forward slash character (“/”) is not permitted. Names beginning with “innodb_” are reserved for special use.

The TABLESPACE option may be used to assign InnoDB table partitions or subpartitions to a general tablespace, a separate file-per-table tablespace, or the system tablespace. TABLESPACE option support for table partitions and subpartitions was added in MySQL 5.7. All partitions must belong to the same storage engine.

A tablespace specified at the table level becomes the default tablespace for new partitions and subpartitions. The default tablespace may be overridden by specifying a tablespace at the partition or subpartition level in a CREATE TABLE or ALTER TABLE statement. The following example shows tablespaces defined at the table level and partition level.

mysql> CREATE TABLE t1 ( a INT NOT NULL, PRIMARY KEY (a))
    -> ENGINE=InnoDB TABLESPACE ts1                          
    -> PARTITION BY RANGE (a) PARTITIONS 3 (
    -> PARTITION P1 VALUES LESS THAN (2),
    -> PARTITION P2 VALUES LESS THAN (4) TABLESPACE ts2,
    -> PARTITION P3 VALUES LESS THAN (6) TABLESPACE ts3);

For more information about the TABLESPACE option and partitioning, see Section 15.7.9, “InnoDB General Tablespaces”

To create a table in the system tablespace, specify innodb_system as the tablespace name.

CREATE TABLE tbl_name ... TABLESPACE [=] innodb_system

Using the TABLESPACE [=] innodb_system option, you can place a table of any uncompressed row format in the system tablespace regardless of the innodb_file_per_table setting. For example, you can add a table with ROW_FORMAT=DYNAMIC to the system tablespace using the TABLESPACE [=] innodb_system option.

To create a table in a file-per-table tablespace, specify innodb_file_per_table as the tablespace name.

CREATE TABLE tbl_name ... TABLESPACE [=] innodb_file_per_table

The DATA DIRECTORY clause is permitted with CREATE TABLE ... TABLESPACE=innodb_file_per_table but is otherwise not supported for use in combination with the TABLESPACE option.

The TABLESPACE option is supported with ALTER TABLE and ALTER TABLE ... REORGANIZE PARTITION statements, which can be used to move tables and partitions from one tablespace to another, respectively. For more information, see Section 15.7.9, “InnoDB General Tablespaces”.

The STORAGE table option is employed only with NDB tables. STORAGE determines the type of storage used (disk or memory), and can be one of DISK, MEMORY, or DEFAULT.

TABLESPACE ... STORAGE DISK assigns a table to a MySQL Cluster Disk Data tablespace. The tablespace must already have been created using CREATE TABLESPACE. See Section 21.5.13, “NDB Cluster Disk Data Tables”, for more information.

UNION

Used to access a collection of identical MyISAM tables as one. This works only with MERGE tables. See Section 16.7, “The MERGE Storage Engine”.

You must have SELECT, UPDATE, and DELETE privileges for the tables you map to a MERGE table.

PARTITION BY

If used, a partition_options clause begins with PARTITION BY. This clause contains the function that is used to determine the partition; the function returns an integer value ranging from 1 to num, where num is the number of partitions. (The maximum number of user-defined partitions which a table may contain is 1024; the number of subpartitions—discussed later in this section—is included in this maximum.)

HASH(expr)

Hashes one or more columns to create a key for placing and locating rows. expr is an expression using one or more table columns. This can be any valid MySQL expression (including MySQL functions) that yields a single integer value. For example, these are both valid CREATE TABLE statements using PARTITION BY HASH:

CREATE TABLE t1 (col1 INT, col2 CHAR(5))
    PARTITION BY HASH(col1);

CREATE TABLE t1 (col1 INT, col2 CHAR(5), col3 DATETIME)
    PARTITION BY HASH ( YEAR(col3) );

You may not use either VALUES LESS THAN or VALUES IN clauses with PARTITION BY HASH.

PARTITION BY HASH uses the remainder of expr divided by the number of partitions (that is, the modulus). For examples and additional information, see Section 22.2.4, “HASH Partitioning”.

The LINEAR keyword entails a somewhat different algorithm. In this case, the number of the partition in which a row is stored is calculated as the result of one or more logical AND operations. For discussion and examples of linear hashing, see Section 22.2.4.1, “LINEAR HASH Partitioning”.

KEY(column_list)

This is similar to HASH, except that MySQL supplies the hashing function so as to guarantee an even data distribution. The column_list argument is simply a list of 1 or more table columns (maximum: 16). This example shows a simple table partitioned by key, with 4 partitions:

CREATE TABLE tk (col1 INT, col2 CHAR(5), col3 DATE)
    PARTITION BY KEY(col3)
    PARTITIONS 4;

For tables that are partitioned by key, you can employ linear partitioning by using the LINEAR keyword. This has the same effect as with tables that are partitioned by HASH. That is, the partition number is found using the & operator rather than the modulus (see Section 22.2.4.1, “LINEAR HASH Partitioning”, and Section 22.2.5, “KEY Partitioning”, for details). This example uses linear partitioning by key to distribute data between 5 partitions:

CREATE TABLE tk (col1 INT, col2 CHAR(5), col3 DATE)
    PARTITION BY LINEAR KEY(col3)
    PARTITIONS 5;

The ALGORITHM={1|2} option is supported with [SUB]PARTITION BY [LINEAR] KEY beginning with MySQL 5.7.1. ALGORITHM=1 causes the server to use the same key-hashing functions as MySQL 5.1; ALGORITHM=2 means that the server employs the key-hashing functions implemented and used by default for new KEY partitioned tables in MySQL 5.5 and later. (Partitioned tables created with the key-hashing functions employed in MySQL 5.5 and later cannot be used by a MySQL 5.1 server.) Not specifying the option has the same effect as using ALGORITHM=2. This option is intended for use chiefly when upgrading or downgrading [LINEAR] KEY partitioned tables between MySQL 5.1 and later MySQL versions, or for creating tables partitioned by KEY or LINEAR KEY on a MySQL 5.5 or later server which can be used on a MySQL 5.1 server. For more information, see Section 14.1.8.1, “ALTER TABLE Partition Operations”.

mysqldump in MySQL 5.7 (and later) writes this option encased in versioned comments, like this:

CREATE TABLE t1 (a INT)
/*!50100 PARTITION BY KEY */ /*!50611 ALGORITHM = 1 */ /*!50100 ()
      PARTITIONS 3 */

This causes MySQL 5.6.10 and earlier servers to ignore the option, which would otherwise cause a syntax error in those versions. If you plan to load a dump made on a MySQL 5.7 server where you use tables that are partitioned or subpartitioned by KEY into a MySQL 5.6 server previous to version 5.6.11, be sure to consult Changes Affecting Upgrades to MySQL 5.6, before proceeding. (The information found there also applies if you are loading a dump containing KEY partitioned or subpartitioned tables made from a MySQL 5.7—actually 5.6.11 or later—server into a MySQL 5.5.30 or earlier server.)

Also in MySQL 5.6.11 and later, ALGORITHM=1 is shown when necessary in the output of SHOW CREATE TABLE using versioned comments in the same manner as mysqldump. ALGORITHM=2 is always omitted from SHOW CREATE TABLE output, even if this option was specified when creating the original table.

You may not use either VALUES LESS THAN or VALUES IN clauses with PARTITION BY KEY.

RANGE(expr)

In this case, expr shows a range of values using a set of VALUES LESS THAN operators. When using range partitioning, you must define at least one partition using VALUES LESS THAN. You cannot use VALUES IN with range partitioning.

Suppose that you have a table that you wish to partition on a column containing year values, according to the following scheme.

A table implementing such a partitioning scheme can be realized by the CREATE TABLE statement shown here:

CREATE TABLE t1 (
    year_col  INT,
    some_data INT
)
PARTITION BY RANGE (year_col) (
    PARTITION p0 VALUES LESS THAN (1991),
    PARTITION p1 VALUES LESS THAN (1995),
    PARTITION p2 VALUES LESS THAN (1999),
    PARTITION p3 VALUES LESS THAN (2002),
    PARTITION p4 VALUES LESS THAN (2006),
    PARTITION p5 VALUES LESS THAN MAXVALUE
);

PARTITION ... VALUES LESS THAN ... statements work in a consecutive fashion. VALUES LESS THAN MAXVALUE works to specify “leftover” values that are greater than the maximum value otherwise specified.

VALUES LESS THAN clauses work sequentially in a manner similar to that of the case portions of a switch ... case block (as found in many programming languages such as C, Java, and PHP). That is, the clauses must be arranged in such a way that the upper limit specified in each successive VALUES LESS THAN is greater than that of the previous one, with the one referencing MAXVALUE coming last of all in the list.

RANGE COLUMNS(column_list)

This variant on RANGE facilitates partition pruning for queries using range conditions on multiple columns (that is, having conditions such as WHERE a = 1 AND b < 10 or WHERE a = 1 AND b = 10 AND c < 10). It enables you to specify value ranges in multiple columns by using a list of columns in the COLUMNS clause and a set of column values in each PARTITION ... VALUES LESS THAN (value_list) partition definition clause. (In the simplest case, this set consists of a single column.) The maximum number of columns that can be referenced in the column_list and value_list is 16.

The column_list used in the COLUMNS clause may contain only names of columns; each column in the list must be one of the following MySQL data types: the integer types; the string types; and time or date column types. Columns using BLOB, TEXT, SET, ENUM, BIT, or spatial data types are not permitted; columns that use floating-point number types are also not permitted. You also may not use functions or arithmetic expressions in the COLUMNS clause.

The VALUES LESS THAN clause used in a partition definition must specify a literal value for each column that appears in the COLUMNS() clause; that is, the list of values used for each VALUES LESS THAN clause must contain the same number of values as there are columns listed in the COLUMNS clause. An attempt to use more or fewer values in a VALUES LESS THAN clause than there are in the COLUMNS clause causes the statement to fail with the error Inconsistency in usage of column lists for partitioning.... You cannot use NULL for any value appearing in VALUES LESS THAN. It is possible to use MAXVALUE more than once for a given column other than the first, as shown in this example:

CREATE TABLE rc (
    a INT NOT NULL,
    b INT NOT NULL
)
PARTITION BY RANGE COLUMNS(a,b) (
    PARTITION p0 VALUES LESS THAN (10,5),
    PARTITION p1 VALUES LESS THAN (20,10),
    PARTITION p2 VALUES LESS THAN (50,MAXVALUE),
    PARTITION p3 VALUES LESS THAN (65,MAXVALUE),
    PARTITION p4 VALUES LESS THAN (MAXVALUE,MAXVALUE)
);

Each value used in a VALUES LESS THAN value list must match the type of the corresponding column exactly; no conversion is made. For example, you cannot use the string '1' for a value that matches a column that uses an integer type (you must use the numeral 1 instead), nor can you use the numeral 1 for a value that matches a column that uses a string type (in such a case, you must use a quoted string: '1').

For more information, see Section 22.2.1, “RANGE Partitioning”, and Section 22.4, “Partition Pruning”.

LIST(expr)

This is useful when assigning partitions based on a table column with a restricted set of possible values, such as a state or country code. In such a case, all rows pertaining to a certain state or country can be assigned to a single partition, or a partition can be reserved for a certain set of states or countries. It is similar to RANGE, except that only VALUES IN may be used to specify permissible values for each partition.

VALUES IN is used with a list of values to be matched. For instance, you could create a partitioning scheme such as the following:

CREATE TABLE client_firms (
    id   INT,
    name VARCHAR(35)
)
PARTITION BY LIST (id) (
    PARTITION r0 VALUES IN (1, 5, 9, 13, 17, 21),
    PARTITION r1 VALUES IN (2, 6, 10, 14, 18, 22),
    PARTITION r2 VALUES IN (3, 7, 11, 15, 19, 23),
    PARTITION r3 VALUES IN (4, 8, 12, 16, 20, 24)
);

When using list partitioning, you must define at least one partition using VALUES IN. You cannot use VALUES LESS THAN with PARTITION BY LIST.

LIST COLUMNS(column_list)

This variant on LIST facilitates partition pruning for queries using comparison conditions on multiple columns (that is, having conditions such as WHERE a = 5 AND b = 5 or WHERE a = 1 AND b = 10 AND c = 5). It enables you to specify values in multiple columns by using a list of columns in the COLUMNS clause and a set of column values in each PARTITION ... VALUES IN (value_list) partition definition clause.

The rules governing regarding data types for the column list used in LIST COLUMNS(column_list) and the value list used in VALUES IN(value_list) are the same as those for the column list used in RANGE COLUMNS(column_list) and the value list used in VALUES LESS THAN(value_list), respectively, except that in the VALUES IN clause, MAXVALUE is not permitted, and you may use NULL.

There is one important difference between the list of values used for VALUES IN with PARTITION BY LIST COLUMNS as opposed to when it is used with PARTITION BY LIST. When used with PARTITION BY LIST COLUMNS, each element in the VALUES IN clause must be a set of column values; the number of values in each set must be the same as the number of columns used in the COLUMNS clause, and the data types of these values must match those of the columns (and occur in the same order). In the simplest case, the set consists of a single column. The maximum number of columns that can be used in the column_list and in the elements making up the value_list is 16.

The table defined by the following CREATE TABLE statement provides an example of a table using LIST COLUMNS partitioning:

CREATE TABLE lc (
    a INT NULL,
    b INT NULL
)
PARTITION BY LIST COLUMNS(a,b) (
    PARTITION p0 VALUES IN( (0,0), (NULL,NULL) ),
    PARTITION p1 VALUES IN( (0,1), (0,2), (0,3), (1,1), (1,2) ),
    PARTITION p2 VALUES IN( (1,0), (2,0), (2,1), (3,0), (3,1) ),
    PARTITION p3 VALUES IN( (1,3), (2,2), (2,3), (3,2), (3,3) )
);

PARTITIONS num

The number of partitions may optionally be specified with a PARTITIONS num clause, where num is the number of partitions. If both this clause and any PARTITION clauses are used, num must be equal to the total number of any partitions that are declared using PARTITION clauses.

SUBPARTITION BY

A partition may optionally be divided into a number of subpartitions. This can be indicated by using the optional SUBPARTITION BY clause. Subpartitioning may be done by HASH or KEY. Either of these may be LINEAR. These work in the same way as previously described for the equivalent partitioning types. (It is not possible to subpartition by LIST or RANGE.)

The number of subpartitions can be indicated using the SUBPARTITIONS keyword followed by an integer value.

Rigorous checking of the value used in PARTITIONS or SUBPARTITIONS clauses is applied and this value must adhere to the following rules:

partition_definition

Each partition may be individually defined using a partition_definition clause. The individual parts making up this clause are as follows:

subpartition_definition

The partition definition may optionally contain one or more subpartition_definition clauses. Each of these consists at a minimum of the SUBPARTITION name, where name is an identifier for the subpartition. Except for the replacement of the PARTITION keyword with SUBPARTITION, the syntax for a subpartition definition is identical to that for a partition definition.

Subpartitioning must be done by HASH or KEY, and can be done only on RANGE or LIST partitions. See Section 22.2.6, “Subpartitioning”.

Considerations for InnoDB

Considerations for NDB Cluster

Options

Notes

InnoDB Examples

NDB Example

EXTENT_SIZE is rounded up to the nearest whole multiple of 32K.

INITIAL_SIZE is rounded down to the nearest whole multiple of 32K; this result is rounded up to the nearest whole multiple of EXTENT_SIZE (after any rounding).

ADD DATAFILE: Defines the name of a tablespace data file; this option is always required. An InnoDB tablespace supports only a single data file, whose name must include a .ibd extension. A MySQL Cluster tablespace supports multiple data files which can have any legal file names; more data files can be added to a MySQL Cluster tablespace following its creation by using an ALTER TABLESPACE statement.

To place the data file in a location outside of the MySQL data directory (datadir), include an absolute directory path or a path relative to the MySQL data directory. If you do not specify a path, the tablespace is created in the MySQL data directory. An isl file is created in the MySQL data directory when an InnoDB tablespace is created outside of the MySQL data directory.

To avoid conflicts with implicitly created file-per-table tablespaces, creating a general tablespace in a subdirectory under the MySQL data directory is not supported. Also, when creating a general tablespace outside of the MySQL data directory, the directory must exist prior to creating the tablespace.

The file_name, including the path (optional), must be quoted with single or double quotations marks. File names (not counting any “.ibd” extension for InnoDB files) and directory names must be at least one byte in length. Zero length file names and directory names are not supported.

FILE_BLOCK_SIZE: This option—which is specific to InnoDB, and is ignored by NDB—defines the block size for the tablespace data file. If you do not specify this option, FILE_BLOCK_SIZE defaults to innodb_page_size. FILE_BLOCK_SIZE is required when you intend to use the tablespace for storing compressed InnoDB tables (ROW_FORMAT=COMPRESSED).