13.1.17.1 CREATE TABLE ... LIKE Syntax

13.1.17.2 CREATE TABLE ... SELECT Syntax

13.1.17.3 Using FOREIGN KEY Constraints

13.1.17.4 Silent Column Specification Changes

CREATE TABLE does not automatically commit the current active transaction if you use the TEMPORARY keyword.

TEMPORARY tables have a very loose relationship with databases (schemas). Dropping a database does not automatically drop any TEMPORARY tables created within that database. Also, you can create a TEMPORARY table in a nonexistent database if you qualify the table name with the database name in the CREATE TABLE statement. In this case, all subsequent references to the table must be qualified with the database name.

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

• 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 12.14, “Information Functions”, and Section 23.8.7.37, “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 5.1.7, “Server SQL Modes”.

  Note

  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 3.6.9, “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 5.1.4, “Server System Variables”.

  For information about InnoDB and AUTO_INCREMENT, see Section 14.8.6, “AUTO_INCREMENT Handling in InnoDB”. For information about AUTO_INCREMENT and MySQL Replication, see Section 17.4.1.1, “Replication and AUTO_INCREMENT”.

• Character data types (CHAR, VARCHAR, TEXT) can include CHARACTER SET and COLLATE attributes to specify the character set and collation for the column. For details, see Section 10.1, “Character Set Support”. CHARSET is a synonym forCHARACTER SET. Example:

  CREATE TABLE t (c CHAR(20) CHARACTER SET utf8 COLLATE utf8_bin);
  

  MySQL 5.6 interprets length specifications in character column definitions in characters. Lengths for BINARY and VARBINARY are in bytes.

• The DEFAULT clause 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 (as of MySQL 5.6.5) DATETIME column. See Section 11.3.5, “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 11.6, “Data Type Default Values”.

  BLOB and TEXT 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. (Before MySQL 5.6.6, the statement produces an error even if strict mode is not enabled.)

• 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.

• 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).

  For NDB tables, the default value for COLUMN_FORMAT is DEFAULT.

  COLUMN_FORMAT currently has no effect on columns of tables using storage engines other than NDB. In MySQL 5.6 and later, COLUMN_FORMAT is silently ignored.

• For NDB tables, it is also 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.

• 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.

• 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.

• A PRIMARY KEY is 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 aPRIMARY 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 14.8.9, “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 or UNIQUE index 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 13.7.5.23, “SHOW INDEX Syntax”.

• 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 values specify additional options for an index. USING is one such option. For details about permissible index_option values, see Section 13.1.13, “CREATE INDEX Syntax”.

  For more information about indexes, see Section 8.3.1, “How MySQL Uses Indexes”.

• In MySQL 5.6, 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.

• For CHAR, VARCHAR, BINARY, and VARBINARY columns, indexes can be created that use only the leading part of column values, using col_name(length) syntax to specify an index prefix length. BLOB and TEXT columns also can be indexed, but a prefix length must be given. Prefix lengths are given in characters for nonbinary string types and in bytes for binary string types. That is, index entries consist of the first length characters of each column value for CHAR, VARCHAR, andTEXT columns, and the first length bytes of each column value for BINARY, VARBINARY, and BLOB columns. Indexing only a prefix of column values like this can make the index file much smaller. For additional information about index prefixes, see Section 13.1.13, “CREATE INDEX Syntax”.

  Only the InnoDB and MyISAM storage engines support indexing on BLOB and TEXT columns. For example:

  CREATE TABLE test (blob_col BLOB, INDEX(blob_col(10)));
  

  Prefixes can be up to 767 bytes long for InnoDB tables or 3072 bytes if the innodb_large_prefix option is enabled.

  Note

  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.

• An index_col_name specification can end with ASC or DESC. These keywords are permitted for future extensions for specifying ascending or descending index value storage. Currently, they are parsed but ignored; index values are always stored in ascending order.

• When you use ORDER BY or GROUP BY on a column in a SELECT, the server sorts values using only the initial number of bytes indicated by the max_sort_length system variable.

• You can create special FULLTEXT indexes, which are 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 12.9, “Full-Text Search Functions”, for details of operation. A WITH PARSER clause can be specified as anindex_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. See Section 24.2, “The MySQL Plugin API”, for details on creating plugins.

• You can create SPATIAL indexes on spatial data types. Spatial types are supported only for MyISAM tables and indexed columns must be declared as NOT NULL. See Section 11.5, “Extensions for Spatial Data”.

• In MySQL 5.6, index definitions can include an optional comment of up to 1024 characters.

• 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 13.1.17.3, “Using FOREIGN KEY Constraints”. For information specific to foreign keys in InnoDB, see Section 14.8.7, “InnoDB and FOREIGN KEY Constraints”.

  For other storage engines, MySQL Server parses and ignores the FOREIGN KEY and REFERENCES syntax in CREATE TABLE statements. The CHECK clause is parsed but ignored by all storage engines. See Section 1.7.2.3, “Foreign Key Differences”.

  Important

  For users familiar with the ANSI/ISO SQL Standard, please note that no storage engine, including InnoDB, recognizes or enforces the MATCH clause used in referential integrity constraint definitions. Use of an explicitMATCH clause will not have the specified effect, and also causes ON DELETE and ON UPDATE clauses to be ignored. For these reasons, specifying MATCH should be avoided.

  The MATCH clause in the SQL standard controls how NULL values in a composite (multiple-column) foreign key are handled when comparing to a primary key. InnoDB essentially implements the semantics defined byMATCH SIMPLE, which permit a foreign key to be all or partially NULL. In that case, the (child table) row containing such a foreign key is permitted to be inserted, and does not match any row in the referenced (parent) table. It is possible to implement other semantics using triggers.

  Additionally, MySQL requires that the referenced columns be indexed for performance. However, it does not enforce any requirement that the referenced columns be declared UNIQUE or NOT NULL. The handling of foreign key references to nonunique keys or keys that contain NULL values is not well defined for operations such as UPDATE or DELETE CASCADE. You are advised to use foreign keys that reference only keys that are both UNIQUE (or PRIMARY) and NOT NULL.

  MySQL parses but ignores “inline REFERENCES specifications” (as defined in the SQL standard) where the references are defined as part of the column specification. MySQL accepts REFERENCES clauses only when specified as part of a separate FOREIGN KEY specification.

  Note

  Partitioned tables employing the InnoDB storage engine do not support foreign keys. NDB tables that are partitioned by KEY or LINEAR KEY are not affected by this restriction. See Section 19.6, “Restrictions and Limitations on Partitioning”, for more information.

• There is a hard limit of 4096 columns per table, but the effective maximum may be less for a given table and depends on the factors discussed in Section C.10.4, “Limits on Table Column Count and Row Size”.

A STORAGE clause cannot be used in a CREATE TABLE statement without a TABLESPACE clause.

The older TYPE option that was synonymous with ENGINE was removed in MySQL 5.5. When upgrading to MySQL 5.5 or later, you must convert existing applications that rely on TYPE to use ENGINE instead.

• AUTO_INCREMENT

  The initial AUTO_INCREMENT value for the table. In MySQL 5.6, 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 5.1.4, “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

  Specify 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

  Specify a default collation for the table.

• COMMENT

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

• CONNECTION

  The connection string for a FEDERATED table.

  Note

  Older versions of MySQL used a COMMENT option for the connection string.

• 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 14.7.5, “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 InnoDBtables, 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.

  Important

  Table-level DATA DIRECTORY and INDEX DIRECTORY options are ignored for partitioned tables. (Bug #32091)

  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 8.12.4.2, “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.

  Important

  You cannot use path names that contain the MySQL data directory with DATA DIRECTORY or INDEX DIRECTORY. This includes partitioned tables and individual table partitions. (See Bug #32167.)

• 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 5.1.4, “Server System Variables”. (MyISAM only.)

• 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 15.7, “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, possibleKEY_BLOCK_SIZE values include 0, 1, 2, 4, 8, and 16. See 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.

• 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

  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:

  • Every key needs one extra byte to indicate how many bytes of the previous key are the same for the next key.

  • The pointer to the row is stored in high-byte-first order directly after the key, to improve 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 takesstorage_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. The choices differ depending on the storage engine used for the table.

  For InnoDB tables:

  • Rows are stored in compact format (ROW_FORMAT=COMPACT) by default.

  • The noncompact format used in older versions of MySQL can still be requested by specifying ROW_FORMAT=REDUNDANT.

  • To enable compression for InnoDB tables, specify ROW_FORMAT=COMPRESSED and follow the procedures in Section 14.9, “InnoDB Table Compression”.

  • For more efficient InnoDB storage of data types, especially BLOB types, specify ROW_FORMAT=DYNAMIC and follow the procedures in Section 14.11.3, “DYNAMIC and COMPRESSED Row Formats”. Both the COMPRESSED and DYNAMIC row formats require creating the table with the configuration settings innodb_file_per_table=1 and innodb_file_format=barracuda.

  • When you specify a non-default ROW_FORMAT clause, consider also enabling the innodb_strict_mode configuration option.

  • ROW_FORMAT=FIXED is not supported. If ROW_FORMAT=FIXED is specified while innodb_strict_mode is disabled, InnoDB issues a warning and assumes ROW_FORMAT=COMPACT. If ROW_FORMAT=FIXED is specified whileinnodb_strict_mode is enabled, InnoDB returns an error.

  • For additional information about InnoDB row formats, see Section 14.11, “InnoDB Row Storage and Row Formats”.

  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 15.2.3, “MyISAM Table Storage Formats”.

  Note

  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.

• 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 14.6.11.1, “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 14.6.11.1, “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 14.6.11.1, “Configuring Persistent Optimizer Statistics Parameters”.

• UNION

  UNION is used when you want to access a collection of identical MyISAM tables as one. This works only with MERGE tables. See Section 15.7, “The MERGE Storage Engine”.

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

  Note

  Formerly, all tables used had to be in the same database as the MERGE table itself. This restriction no longer applies.

Not all options shown in the syntax for partition_options at the beginning of this section are available for all partitioning types. Please see the listings for the following individual types for information specific to each type, and see Chapter 19, Partitioning, for more complete information about the workings of and uses for partitioning in MySQL, as well as additional examples of table creation and other statements relating to MySQL partitioning.

• 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 19.2.4, “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 19.2.4.1, “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 19.2.4.1, “LINEAR HASH Partitioning”, and Section 19.2.5, “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 5.6.11. 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 13.1.7.1, “ALTER TABLE Partition Operations”.

  mysqldump in MySQL 5.6.11 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 5.5.31 or later MySQL 5.5 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 Section 2.11.1.1, “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 5.6.11 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 TABLEoutput, 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.

  Note

  For tables partitioned by RANGE, VALUES LESS THAN must be used with either an integer literal value or an expression that evaluates to a single integer value. In MySQL 5.6, you can overcome this limitation in a table that is defined using PARTITION BY RANGE COLUMNS, as described later in this section.

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

  Partition Number:	Years Range:
  0	1990 and earlier
  1	1991 to 1994
  2	1995 to 1998
  3	1999 to 2002
  4	2003 to 2005
  5	2006 and later

  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 usingBLOB, 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 (MAXVALUE,15),
  
      PARTITION p3 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 19.2.1, “RANGE Partitioning”, and Section 19.4, “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.

  Note

  For tables partitioned by LIST, the value list used with VALUES IN must consist of integer values only. In MySQL 5.6, you can overcome this limitation using partitioning by LIST COLUMNS, which is described later in this section.

• 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) )
  
  );
  

• 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.

  Note

  Whether or not you use a PARTITIONS clause in creating a table that is partitioned by RANGE or LIST, you must still include at least one PARTITION VALUES clause in the table definition (see below).

• 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:

  • The value must be a positive, nonzero integer.

  • No leading zeros are permitted.

  • The value must be an integer literal, and cannot not be an expression. For example, PARTITIONS 0.2E+01 is not permitted, even though 0.2E+01 evaluates to 2. (Bug #15890)

The expression (expr) used in a PARTITION BY clause cannot refer to any columns not in the table being created; such references are specifically not permitted and cause the statement to fail with an error. (Bug #29444)

• PARTITION partition_name: This specifies a logical name for the partition.

• A VALUES clause: For range partitioning, each partition must include a VALUES LESS THAN clause; for list partitioning, you must specify a VALUES IN clause for each partition. This is used to determine which rows are to be stored in this partition. See the discussions of partitioning types in Chapter 19, Partitioning, for syntax examples.

• An optional COMMENT clause may be used to specify a string that describes the partition. Example:

  COMMENT = 'Data for the years previous to 1999'
  

  Beginning with MySQL 5.6.6, the maximum length for a partition comment is 1024 characters. (Previously, this limit was not explicitly defined.)

• DATA DIRECTORY and INDEX DIRECTORY may be used to indicate the directory where, respectively, the data and indexes for this partition are to be stored. Both the data_dir and the index_dir must be absolute system path names. Example:

  CREATE TABLE th (id INT, name VARCHAR(30), adate DATE)
  
  PARTITION BY LIST(YEAR(adate))
  
  (
  
    PARTITION p1999 VALUES IN (1995, 1999, 2003)
  
      DATA DIRECTORY = '/var/appdata/95/data'
  
      INDEX DIRECTORY = '/var/appdata/95/idx',
  
    PARTITION p2000 VALUES IN (1996, 2000, 2004)
  
      DATA DIRECTORY = '/var/appdata/96/data'
  
      INDEX DIRECTORY = '/var/appdata/96/idx',
  
    PARTITION p2001 VALUES IN (1997, 2001, 2005)
  
      DATA DIRECTORY = '/var/appdata/97/data'
  
      INDEX DIRECTORY = '/var/appdata/97/idx',
  
    PARTITION p2002 VALUES IN (1998, 2002, 2006)
  
      DATA DIRECTORY = '/var/appdata/98/data'
  
      INDEX DIRECTORY = '/var/appdata/98/idx'
  
  );
  

  DATA DIRECTORY and INDEX DIRECTORY behave in the same way as in the CREATE TABLE statement's table_option clause as used for MyISAM tables.

  One data directory and one index directory may be specified per partition. If left unspecified, the data and indexes are stored by default in the table's database directory.

  On Windows, the DATA DIRECTORY and INDEX DIRECTORY options are not supported for individual partitions or subpartitions of MyISAM tables, and the INDEX DIRECTORY option is not supported for individual partitions or subpartitions of InnoDB tables. These options are ignored on Windows, except that a warning is generated. (Bug #30459)

  Note

  The DATA DIRECTORY and INDEX DIRECTORY options are ignored for creating partitioned tables if NO_DIR_IN_CREATE is in effect. (Bug #24633)

• MAX_ROWS and MIN_ROWS may be used to specify, respectively, the maximum and minimum number of rows to be stored in the partition. The values for max_number_of_rows and min_number_of_rows must be positive integers. As with the table-level options with the same names, these act only as “suggestions” to the server and are not hard limits.

• The optional TABLESPACE clause may be used to designate a tablespace for the partition. Used for MySQL Cluster only.

• The partitioning handler accepts a [STORAGE] ENGINE option for both PARTITION and SUBPARTITION. Currently, the only way in which this can be used is to set all partitions or all subpartitions to the same storage engine, and an attempt to set different storage engines for partitions or subpartitions in the same table will give rise to the error ERROR 1469 (HY000): The mix of handlers in the partitions is not permitted in this version of MySQL. We expect to lift this restriction on partitioning in a future MySQL release.

• 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 19.2.6, “Subpartitioning”.

The original CREATE TABLE statement, including all specifications and table options are stored by MySQL when the table is created. The information is retained so that if you change storage engines, collations or other settings using an ALTER TABLE statement, the original table options specified are retained. This enables you to change between InnoDB and MyISAM table types even though the row formats supported by the two engines are different.

Because the text of the original statement is retained, but due to the way that certain values and options may be silently reconfigured (such as the ROW_FORMAT), the active table definition (accessible through DESCRIBE or with SHOW TABLE STATUS) and the table creation string (accessible through SHOW CREATE TABLE) will report different values.

http://dev.mysql.com/doc/refman/5.6/en/create-table.html