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Excerpts from this Manual

13.1.17 CREATE TABLE Syntax



    { LIKE old_tbl_name | (LIKE old_tbl_name) }

    col_name column_definition
  | [CONSTRAINT [symbol]] PRIMARY KEY [index_type] (index_col_name,...)
      [index_option] ...
  | {INDEX|KEY} [index_name] [index_type] (index_col_name,...)
      [index_option] ...
      [index_name] [index_type] (index_col_name,...)
      [index_option] ...
  | {FULLTEXT|SPATIAL} [INDEX|KEY] [index_name] (index_col_name,...)
      [index_option] ...
      [index_name] (index_col_name,...) reference_definition
  | CHECK (expr)

    data_type [NOT NULL | NULL] [DEFAULT default_value]
      [COMMENT 'string']

  | INT[(length)] [UNSIGNED] [ZEROFILL]
  | REAL[(length,decimals)] [UNSIGNED] [ZEROFILL]
  | DOUBLE[(length,decimals)] [UNSIGNED] [ZEROFILL]
  | FLOAT[(length,decimals)] [UNSIGNED] [ZEROFILL]
  | DECIMAL[(length[,decimals])] [UNSIGNED] [ZEROFILL]
  | NUMERIC[(length[,decimals])] [UNSIGNED] [ZEROFILL]
  | DATE
  | TIME[(fsp)]
  | TIMESTAMP[(fsp)]
  | DATETIME[(fsp)]
  | YEAR
  | CHAR[(length)] [BINARY]
      [CHARACTER SET charset_name] [COLLATE collation_name]
  | VARCHAR(length) [BINARY]
      [CHARACTER SET charset_name] [COLLATE collation_name]
  | BINARY[(length)]
  | VARBINARY(length)
  | BLOB
      [CHARACTER SET charset_name] [COLLATE collation_name]
      [CHARACTER SET charset_name] [COLLATE collation_name]
      [CHARACTER SET charset_name] [COLLATE collation_name]
      [CHARACTER SET charset_name] [COLLATE collation_name]
  | ENUM(value1,value2,value3,...)
      [CHARACTER SET charset_name] [COLLATE collation_name]
  | SET(value1,value2,value3,...)
      [CHARACTER SET charset_name] [COLLATE collation_name]
  | spatial_type

    col_name [(length)] [ASC | DESC]


    KEY_BLOCK_SIZE [=] value
  | index_type
  | WITH PARSER parser_name
  | COMMENT 'string'

    REFERENCES tbl_name (index_col_name,...)
      [ON DELETE reference_option]
      [ON UPDATE reference_option]


    table_option [[,] table_option] ...

    ENGINE [=] engine_name
  | AUTO_INCREMENT [=] value
  | AVG_ROW_LENGTH [=] value
  | [DEFAULT] CHARACTER SET [=] charset_name
  | CHECKSUM [=] {0 | 1}
  | [DEFAULT] COLLATE [=] collation_name
  | COMMENT [=] 'string'
  | CONNECTION [=] 'connect_string'
  | DATA DIRECTORY [=] 'absolute path to directory'
  | DELAY_KEY_WRITE [=] {0 | 1}
  | INDEX DIRECTORY [=] 'absolute path to directory'
  | KEY_BLOCK_SIZE [=] value
  | MAX_ROWS [=] value
  | MIN_ROWS [=] value
  | PACK_KEYS [=] {0 | 1 | DEFAULT}
  | PASSWORD [=] 'string'
  | STATS_SAMPLE_PAGES [=] value
  | UNION [=] (tbl_name[,tbl_name]...)

        { [LINEAR] HASH(expr)
        | [LINEAR] KEY [ALGORITHM={1|2}] (column_list)
        | RANGE{(expr) | COLUMNS(column_list)}
        | LIST{(expr) | COLUMNS(column_list)} }
    [PARTITIONS num]
        { [LINEAR] HASH(expr)
        | [LINEAR] KEY [ALGORITHM={1|2}] (column_list) }
    [(partition_definition [, partition_definition] ...)]

    PARTITION partition_name
            {LESS THAN {(expr | value_list) | MAXVALUE} 
            IN (value_list)}]
        [[STORAGE] ENGINE [=] engine_name]
        [COMMENT [=] 'comment_text' ]
        [DATA DIRECTORY [=] 'data_dir']
        [INDEX DIRECTORY [=] 'index_dir']
        [MAX_ROWS [=] max_number_of_rows]
        [MIN_ROWS [=] min_number_of_rows]
        [TABLESPACE [=] tablespace_name]
        [NODEGROUP [=] node_group_id]
        [(subpartition_definition [, subpartition_definition] ...)]

    SUBPARTITION logical_name
        [[STORAGE] ENGINE [=] engine_name]
        [COMMENT [=] 'comment_text' ]
        [DATA DIRECTORY [=] 'data_dir']
        [INDEX DIRECTORY [=] 'index_dir']
        [MAX_ROWS [=] max_number_of_rows]
        [MIN_ROWS [=] min_number_of_rows]
        [TABLESPACE [=] tablespace_name]
        [NODEGROUP [=] node_group_id]

    [IGNORE | REPLACE] [AS] SELECT ...   (Some valid select statement)

CREATE TABLE creates a table with the given name. You must have the CREATE privilege for the table.

Rules for permissible table names are given in Section 9.2, “Schema Object Names”. By default, the table is created in the default database, using the InnoDB storage engine. An error occurs if the table exists, if there is no default database, or if the database does not exist.

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`.

Cloning or Copying a Table

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, “CREATE TABLE ... LIKE Syntax”.

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

CREATE TABLE new_tbl SELECT * FROM orig_tbl;

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

Temporary Tables

You can use the TEMPORARY keyword when creating a table. A TEMPORARY table is visible only to the current session, and is dropped automatically when the session is closed. This means that two different sessions can use the same temporary table name without conflicting with each other or with an existing non-TEMPORARY table of the same name. (The existing table is hidden until the temporary table is dropped.) To create temporary tables, you must have the CREATE TEMPORARY TABLES privilege.


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.

Existing Table with Same Name

The keywords IF NOT EXISTS prevent 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.

Physical Representation

MySQL represents each table by an .frm table format (definition) file in the database directory. The storage engine for the table might create other files as well.

For InnoDB tables, the file storage is controlled by the innodb_file_per_table configuration option. When this option is turned off, all InnoDB tables and indexes are stored in the system tablespace, represented by one or more .ibd files. For each InnoDB table created when this option is turned on, the table data and all associated indexes are stored in a .ibd file located inside the database directory.

For MyISAM tables, the storage engine creates data and index files. Thus, for each MyISAM table tbl_name, there are three disk files.

tbl_name.frmTable format (definition) file
tbl_name.MYDData file
tbl_name.MYIIndex file

Chapter 15, Alternative Storage Engines, describes what files each storage engine creates to represent tables. If a table name contains special characters, the names for the table files contain encoded versions of those characters as described in Section 9.2.3, “Mapping of Identifiers to File Names”.

Data Types and Attributes for Columns

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 11, Data Types, and Section 11.5, “Extensions for Spatial Data”.

Some attributes do not apply to all data types. AUTO_INCREMENT applies only to integer and floating-point types. DEFAULT does not apply to the BLOB or TEXT types.

  • 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, “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”.


    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

    For information about InnoDB and AUTO_INCREMENT, see Section 14.5.5, “AUTO_INCREMENT Handling in InnoDB”. For information about AUTO_INCREMENT and MySQL Replication, see Section, “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 for CHARACTER 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 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 14.2.6, “InnoDB Table and Index Structures”.)

  • 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, “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.


    CREATE TABLE lookup
      (id INT, INDEX USING BTREE (id))

    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, and TEXT 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. See Section 8.3.4, “Column Indexes”.

    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.


    Prefix limits are measured in bytes, whereas the prefix length in CREATE TABLE statements is interpreted as number of characters for nonbinary data types (CHAR, VARCHAR, TEXT). Take this into account when specifying a prefix length for a 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 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. 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, “Using FOREIGN KEY Constraints”. For information specific to foreign keys in InnoDB, see Section 14.5.6, “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, “Foreign Key Differences”.


    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 explicit MATCH 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 by MATCH 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.


    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”.

The TABLESPACE and STORAGE table options are employed only with NDB tables. The tablespace named tablespace_name must already have been created using CREATE TABLESPACE. 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. See Section 18.5.12, “MySQL Cluster Disk Data Tables”, for more information.


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

Storage Engines

The ENGINE table option 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.

Storage EngineDescription
InnoDBTransaction-safe tables with row locking and foreign keys. The default storage engine for new tables. See Chapter 14, The InnoDB Storage Engine, and in particular Section 14.1.1, “InnoDB as the Default MySQL Storage Engine” if you have MySQL experience but are new to InnoDB.
MyISAMThe binary portable storage engine that is primarily used for read-only or read-mostly workloads. See Section 15.2, “The MyISAM Storage Engine”.
MEMORYThe data for this storage engine is stored only in memory. See Section 15.3, “The MEMORY Storage Engine”.
CSVTables that store rows in comma-separated values format. See Section 15.4, “The CSV Storage Engine”.
ARCHIVEThe archiving storage engine. See Section 15.5, “The ARCHIVE Storage Engine”.
EXAMPLEAn example engine. See Section 15.9, “The EXAMPLE Storage Engine”.
FEDERATEDStorage engine that accesses remote tables. See Section 15.8, “The FEDERATED Storage Engine”.
HEAPThis is a synonym for MEMORY.
MERGEA collection of MyISAM tables used as one table. Also known as MRG_MyISAM. See Section 15.7, “The MERGE Storage Engine”.
NDBClustered, fault-tolerant, memory-based tables, supporting transactions and foreign keys. Also known as NDBCLUSTER. See Chapter 18, MySQL Cluster NDB 7.3 and MySQL Cluster NDB 7.4.

If a storage engine is specified that is not available, MySQL uses the default engine instead. Normally, this is MyISAM. For example, if a table definition includes the ENGINE=INNODB option but the MySQL server does not support INNODB tables, the table is created as a MyISAM table. This makes it possible to have a replication setup where you have transactional tables on the master but tables created on the slave are nontransactional (to get more speed). In MySQL 5.6, a warning occurs if the storage engine specification is not honored.

Engine substitution can be controlled by the setting of the NO_ENGINE_SUBSTITUTION SQL mode, as described in Section 5.1.7, “Server SQL Modes”.


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.

Optimizing Performance

The other table options are used to optimize the behavior of the table. In most cases, you do not have to specify any of them. These options apply to all storage engines unless otherwise indicated. Options that do not apply to a given storage engine may be accepted and remembered as part of the table definition. Such options then apply if you later use ALTER TABLE to convert the table to use a different storage engine.


    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.


    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.


    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.


    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.)


    Specify a default collation for the table.


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


    The connection string for a FEDERATED table.


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


    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 14.4.5, “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.


    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, “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.


    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.)


    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.)


    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”.


    For compressed InnoDB tables, optionally specifies the size in kilobytes to use for pages. Possible KEY_BLOCK_SIZE values include 0, 1, 2, 4, 8, and 16. The KEY_BLOCK_SIZE value is treated as a hint; a different size could be used by InnoDB if necessary. A value of 0 represents the default compressed page size, which is half of the innodb_page_size value. The KEY_BLOCK_SIZE can only be less than or equal to the innodb_page_size value. If you specify a value greater than the innodb_page_size value, the value is ignored, a warning is issued, and KEY_BLOCK_SIZE is set to half of the innodb_page_size value. If innodb_strict_mode=ON, specifying an invalid KEY_BLOCK_SIZE value returns an error. See Section 14.6, “InnoDB Table Compression” for usage details.

    Individual index definitions can specify a KEY_BLOCK_SIZE value of their own to override the table value.


    Oracle recommends enabling innodb_strict_mode when using the KEY_BLOCK_SIZE clause for InnoDB tables.


    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.


    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:

    • 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 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.)


    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.


    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:

    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”.


    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.


    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, “Configuring Persistent Optimizer Statistics Parameters”.


    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, “Configuring Persistent Optimizer Statistics Parameters”.


    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, “Configuring Persistent Optimizer Statistics Parameters”.


    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.


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

Creating Partitioned Tables

partition_options can be used to control partitioning of the table created with CREATE TABLE.


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.

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.) The choices that are available for this function in MySQL 5.6 are shown in the following list:

  • 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, “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, “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)
        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, “ALTER TABLE Partition Operations”.

    mysqldump in MySQL 5.6.11 and later writes this option encased in versioned comments, like this:

    /*!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, “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 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.


    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:
    01990 and earlier
    11991 to 1994
    21995 to 1998
    31999 to 2002
    42003 to 2005
    52006 and later

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

        year_col  INT,
        some_data INT
    PARTITION BY RANGE (year_col) (

    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:

        a INT NOT NULL, 
        b INT NOT NULL
        PARTITION p1 VALUES LESS THAN (20,10),

    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 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.


    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:

        a INT NULL, 
        b INT NULL
        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.


    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)

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

  • 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 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)


    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”.

Partitions can be modified, merged, added to tables, and dropped from tables. For basic information about the MySQL statements to accomplish these tasks, see Section 13.1.7, “ALTER TABLE Syntax”. For more detailed descriptions and examples, see Section 19.3, “Partition Management”.


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.

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User Comments
  Posted by Martin Friebe on February 22, 2005
I just found a workaround for the limitation of not reopening temp tables (works in 4.1.10 , but wouldn't bet on it in the future);

create temporary table tmp1 (...);

create temporary table tmp2 (...) engine merge union (tmp1);

this will only work if the merge table is temporary itself

add as many merge tables as you need, use the merge tables instead of reopening the tmp (it's still the same table :-) )

they are all temporary, so no clean up necessary.
  Posted by Jeff Donner on August 11, 2005
If you want to the flexibility to drop or modify a foreign key (and, to change properties, you must drop & re-add the new version), you must create the foreign key with an otherwise optional 'symbol' name. You can verify this at the 'alter table syntax' page.
  Posted by Samba Pedapalli on January 2, 2010
Create table with constraints. If you happen to run into "can't create table errno 121" with Error Code 1005, most likely your foreign key name is used by another table's foreign key.

CREATE TABLE IF NOT EXISTS `schema`.`Employee` (
`idEmployee` VARCHAR(45) NOT NULL ,
`Name` VARCHAR(255) NULL ,
`idAddresses` VARCHAR(45) NULL ,
PRIMARY KEY (`idEmployee`) ,
CONSTRAINT `fkEmployee_Addresses`
FOREIGN KEY `fkEmployee_Addresses` (`idAddresses`)
REFERENCES `schema`.`Addresses` (`idAddresses`)
COLLATE = utf8_bin
  Posted by Winfred Qin on August 1, 2010
FOREIGN KEY Constraint Allow Multi-NULL Values -- Not Mentioned by MySQL 5.0 Reference Manual

Compare to UNIQUE KEY Constraint ( the manual says: "For other engines (all but BDB), a UNIQUE index allows multiple NULL values for columns that can contain NULL." ), whether 'allow FOREIGN KEY Constraint to have multi-NULL values' is not mentioned.

By tested on MySQL 5.0 / Ubuntu 8.04, the system says YES, the multi-NULLs are allowed.

I think this should be added to the manual explicitly.
  Posted by Chris Broome on June 9, 2011
As a suggestion, if you're looking to implement some form of alpha-numeric, auto incrementing, primary key you can achieve the same functionality with a regular int-type key. The trick is convert the integer value into a suitable alpha numeric version, ideally through stored functions.

That way when a user requests the alpha numeric value, say '5xzz2', a stored function would translate this into a raw int which would match the id in your table. This approach has the advantage of avoiding maintaining a separate (keyed) varchar column in your tables.

The process to convert a decimal key to an alphanumeric string is essentially the same as converting to a hexadecimal, here's a basic breakdown of a JavaScript version:

You'd just be expanding this algorithm to include as many characters as needed. Here's another example with mysql stored functions for converting a decimal value to a base 36 number (which uses all ten digits and twenty six lower case characters):
  Posted by josé ambriz meza on December 27, 2012
Video en español sobre esta acción de MySQL

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