12.1.5. CREATE TABLE Syntax

[+/-]

12.1.5.1. Silent Column Specification Changes
CREATE [TEMPORARY] TABLE [IF NOT EXISTS] tbl_name
    (create_definition,...)
    [table_options]

Or:

CREATE [TEMPORARY] TABLE [IF NOT EXISTS] tbl_name
    [(create_definition,...)]
    [table_options]
    select_statement

Or:

CREATE [TEMPORARY] TABLE [IF NOT EXISTS] tbl_name
    { LIKE old_tbl_name | (LIKE old_tbl_name) }

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

column_definition:
    data_type [NOT NULL | NULL] [DEFAULT default_value]
      [AUTO_INCREMENT] [UNIQUE [KEY] | [PRIMARY] KEY]
      [COMMENT 'string'] [reference_definition]

data_type:
    TINYINT[(length)] [UNSIGNED] [ZEROFILL]
  | SMALLINT[(length)] [UNSIGNED] [ZEROFILL]
  | MEDIUMINT[(length)] [UNSIGNED] [ZEROFILL]
  | INT[(length)] [UNSIGNED] [ZEROFILL]
  | INTEGER[(length)] [UNSIGNED] [ZEROFILL]
  | BIGINT[(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
  | TIMESTAMP
  | DATETIME
  | YEAR
  | CHAR[(length)]
      [CHARACTER SET charset_name] [COLLATE collation_name]
  | VARCHAR(length)
      [CHARACTER SET charset_name] [COLLATE collation_name]
  | BINARY[(length)]
  | VARBINARY(length)
  | TINYBLOB
  | BLOB
  | MEDIUMBLOB
  | LONGBLOB
  | TINYTEXT [BINARY]
      [CHARACTER SET charset_name] [COLLATE collation_name]
  | TEXT [BINARY]
      [CHARACTER SET charset_name] [COLLATE collation_name]
  | MEDIUMTEXT [BINARY]
      [CHARACTER SET charset_name] [COLLATE collation_name]
  | LONGTEXT [BINARY]
      [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

index_col_name:
    col_name [(length)] [ASC | DESC]

index_type:
    USING {BTREE | HASH | RTREE}

reference_definition:
    REFERENCES tbl_name (index_col_name,...)
      [MATCH FULL | MATCH PARTIAL | MATCH SIMPLE]
      [ON DELETE reference_option]
      [ON UPDATE reference_option]

reference_option:
    RESTRICT | CASCADE | SET NULL | NO ACTION

table_options:
    table_option [[,] table_option] ...

table_option:
    {ENGINE|TYPE} = engine_name
  | AUTO_INCREMENT = value
  | AVG_ROW_LENGTH = value
  | [DEFAULT] CHARACTER SET = charset_name
  | CHECKSUM = {0 | 1}
  | [DEFAULT] COLLATE = collation_name
  | COMMENT = 'string'
  | DATA DIRECTORY = 'absolute path to directory'
  | DELAY_KEY_WRITE = {0 | 1}
  | INDEX DIRECTORY = 'absolute path to directory'
  | INSERT_METHOD = { NO | FIRST | LAST }
  | MAX_ROWS = value
  | MIN_ROWS = value
  | PACK_KEYS = {0 | 1 | DEFAULT}
  | PASSWORD = 'string'
  | RAID_TYPE = { 1 | STRIPED | RAID0 }
      RAID_CHUNKS = value
      RAID_CHUNKSIZE = value
  | ROW_FORMAT = {DEFAULT|DYNAMIC|FIXED|COMPRESSED}
  | UNION = (tbl_name[,tbl_name]...)

select_statement:
    [IGNORE | REPLACE] [AS] SELECT ...   (Some legal select statement)

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

Rules for allowable table names are given in Section 8.2, “Database, Table, Index, Column, and Alias Names”. By default, the table is created in the default database. An error occurs if the table exists, if there is no default database, or if the database does not exist.

In MySQL 3.22 or later, 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`.

From MySQL 3.23 on, you can use the TEMPORARY keyword when creating a table. A TEMPORARY table is visible only to the current connection, and is dropped automatically when the connection is closed. This means that two different connections 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.) From MySQL 4.0.2 on, to create temporary tables, you must have the CREATE TEMPORARY TABLES privilege.

Note

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

In MySQL 3.23 or later, 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.

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

File Purpose
tbl_name.frm Table format (definition) file
tbl_name.MYD Data file
tbl_name.MYI Index file

Chapter 13, Storage Engines, describes what files each storage engine creates to represent tables.

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 10, Data Types, and Chapter 16, Spatial Extensions.

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 11.13, “Information Functions”, and Section 17.6.3.35, “mysql_insert_id()”.

    As of MySQL 4.1.1, 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 5.1.6, “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. As of MySQL 3.23, 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 and BDB 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 13.2.5.3, “AUTO_INCREMENT Handling in InnoDB”.

  • As of MySQL 4.1, 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 9.1, “Character Set Support”. CHARSET is a synonym for CHARACTER SET. Example:

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

    Also as of 4.1, MySQL interprets length specifications in character column definitions in characters. (Earlier versions interpret them in bytes.) Lengths for BINARY and VARBINARY are in bytes.

  • NULL values are handled differently for TIMESTAMP columns than for other column types. Before MySQL 4.1.6, you cannot store a literal NULL in a TIMESTAMP column; setting the column to NULL sets it to the current date and time. Because TIMESTAMP columns behave this way, the NULL and NOT NULL attributes do not apply in the normal way and are ignored if you specify them. On the other hand, to make it easier for MySQL clients to use TIMESTAMP columns, the server reports that such columns can be assigned NULL values (which is true), even though TIMESTAMP never actually contains a NULL value. You can see this when you use DESCRIBE tbl_name to get a description of your table.

    Note that setting a TIMESTAMP column to 0 is not the same as setting it to NULL, because 0 is a valid TIMESTAMP value.

  • 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 column as of MySQL 4.1.2. See Section 10.3.1.2, “TIMESTAMP Properties as of MySQL 4.1”.

    If a column definition includes no explicit DEFAULT value, MySQL determines the default value as described in Section 10.1.4, “Data Type Default Values”.

    BLOB and TEXT columns cannot be assigned a default value.

  • A comment for a column can be specified with the COMMENT option. The comment is displayed by the SHOW CREATE TABLE and SHOW FULL COLUMNS statements. This option is operational as of MySQL 4.1. (It is allowed but ignored in earlier versions.)

  • KEY is normally a synonym for INDEX. From MySQL 4.1, 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. This constraint does not apply to NULL values except for the BDB storage engine. For other engines, a UNIQUE index allows 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. 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, having a long PRIMARY KEY wastes a lot of space. (See Section 13.2.11, “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 (new in MySQL 3.23.11).

  • 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 12.4.5.13, “SHOW INDEX Syntax”.

  • From MySQL 4.1.0 on, some storage engines allow 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;

    For details about USING, see Section 12.1.4, “CREATE INDEX Syntax”.

    For more information about indexes, see Section 7.4.4, “How MySQL Uses Indexes”.

  • Only the MyISAM, InnoDB, BDB, and (as of MySQL 4.0.2) 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 7.4.2, “Column Indexes”.

    Only the MyISAM and (as of MySQL 4.0.14) InnoDB 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 1000 bytes long (767 bytes for InnoDB tables). (Before MySQL 4.1.2, the limit is 255 bytes for all tables.) Note that 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 multi-byte character set.

  • An index_col_name specification can end with ASC or DESC. These keywords are allowed 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 TEXT or BLOB column in a SELECT, the server sorts values using only the initial number of bytes indicated by the max_sort_length system variable. See Section 10.4.3, “The BLOB and TEXT Types”.

  • In MySQL 3.23.23 or later, you can create special FULLTEXT indexes, which are used for full-text searches. Only the MyISAM table type supports 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 11.9, “Full-Text Search Functions”, for details of operation.

  • In MySQL 4.1 or later, 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 Chapter 16, Spatial Extensions.

  • In MySQL 3.23.44 or later, InnoDB tables support checking of foreign key constraints. See Section 13.2, “The InnoDB Storage Engine”. Note that the FOREIGN KEY syntax in InnoDB is more restrictive than the syntax presented for the CREATE TABLE statement at the beginning of this section: The columns of the referenced table must always be explicitly named. InnoDB supports both ON DELETE and ON UPDATE actions on foreign keys as of MySQL 3.23.50 and 4.0.8, respectively. For the precise syntax, see Section 13.2.5.4, “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 1.9.5.6, “Foreign Keys”.

    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 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. Starting from MySQL 3.23.50, InnoDB does not check foreign key constraints on those foreign key or referenced key values that contain a NULL column. InnoDB essentially implements the semantics defined by MATCH SIMPLE, which allow a foreign key to be all or partially NULL. In that case, the (child table) row containing such a foreign key is allowed to be inserted, and does not match any row in the referenced (parent) table.

    Additionally, MySQL and InnoDB require that the referenced columns be indexed for performance. However, the system does not enforce a requirement that the referenced columns be UNIQUE or be declared 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 UNIQUE and NOT NULL keys.

    Furthermore, InnoDB does not recognize or support “inline REFERENCES specifications” (as defined in the SQL standard) where the references are defined as part of the column specification. InnoDB accepts REFERENCES clauses only when specified as part of a separate FOREIGN KEY specification. For other storage engines, MySQL Server parses and ignores foreign key specifications.

  • 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.3.2, “The Maximum Number of Columns Per Table”.

The table_option part of the CREATE TABLE syntax can be used in MySQL 3.23 and above. The = that separates an option name and its value is optional as of MySQL 4.1.

The ENGINE and TYPE options specify the storage engine for the table. ENGINE was added in MySQL 4.0.18 (for 4.0) and 4.1.2 (for 4.1). It is the preferred option name as of those versions, and TYPE has become deprecated. TYPE is supported throughout the 4.x series, but likely will be removed in the future.

The ENGINE and TYPE table options take the storage engine names shown in the following table.

Storage Engine Description
ARCHIVE The archiving storage engine. See Section 13.7, “The ARCHIVE Storage Engine”.
BDB Transaction-safe tables with page locking. Also known as BerkeleyDB. See Section 13.5, “The BDB (BerkeleyDB) Storage Engine”.
CSV Tables that store rows in comma-separated values format. See Section 13.8, “The CSV Storage Engine”.
EXAMPLE An example engine. See Section 13.6, “The EXAMPLE Storage Engine”.
HEAP The data for this table is stored only in memory. See Section 13.4, “The MEMORY (HEAP) Storage Engine”.
ISAM The original MySQL storage engine. See Section 13.10, “The ISAM Storage Engine”.
InnoDB Transaction-safe tables with row locking and foreign keys. See Section 13.2, “The InnoDB Storage Engine”.
MEMORY An alias for HEAP. (Actually, as of MySQL 4.1, MEMORY is the preferred term.)
MERGE A collection of MyISAM tables used as one table. Also known as MRG_MyISAM. See Section 13.3, “The MERGE Storage Engine”.
MyISAM The binary portable storage engine that is the improved replacement for ISAM. See Section 13.1, “The MyISAM Storage Engine”.
NDBCLUSTER Clustered, fault-tolerant, memory-based tables. Also known as NDB. See Chapter 15, MySQL Cluster.

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=BDB option but the MySQL server does not support BDB 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 4.1.1, a warning occurs if the storage engine specification is not honored.

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.

  • AUTO_INCREMENT

    The initial AUTO_INCREMENT value for the table. This works for MyISAM only, for MEMORY as of MySQL 4.1.0, and for InnoDB as of MySQL 4.1.2. 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 do not specify either option, the maximum size for MyISAM data and index files is 4GB. (If your operating system does not support files that large, table sizes are constrained by the operating system limit.) If you want to keep down the pointer sizes to make the index smaller and faster and you do not really need big files, you can decrease the default pointer size by setting the myisam_data_pointer_size system variable, which was added in MySQL 4.1.2. (See Section 5.1.3, “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 may increase the default pointer size by setting this variable. Setting the value to 7 allows 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 60 characters long.

  • DATA DIRECTORY, INDEX DIRECTORY

    By using DATA DIRECTORY='directory' or INDEX DIRECTORY='directory' you can specify where the MyISAM storage engine should put a table's data file and index file. The directory must be the full path name to the directory, not a relative path.

    These options work only for MyISAM tables from MySQL 4.0 on, when you are not using the --skip-symbolic-links option. Your operating system must also have a working, thread-safe realpath() call. See Section 7.6.1.2, “Using Symbolic Links for Tables on Unix”, for more complete information.

    Important

    Beginning with MySQL 4.1.24, you cannot use path names that contain the MySQL data directory with DATA DIRECTORY or INDEX DIRECTORY. (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 5.1.3, “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. This option was introduced in MySQL 4.0.0. See Section 13.3, “The MERGE Storage Engine”.

  • 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.

  • 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 takes storage_size_for_key + pointer_size (where the pointer size is usually 4). Conversely, you get a significant benefit from prefix compression only if you have many numbers that are the same. If all keys are totally different, you use one byte more per key, if the key is not a key that can have NULL values. (In this case, the packed key length is stored in the same byte that is used to mark if a key is NULL.)

  • PASSWORD

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

  • RAID_TYPE

    The RAID_TYPE option can help you to exceed the 2GB/4GB limit for the MyISAM data file (not the index file) on operating systems that do not support big files. This option is unnecessary and not recommended for file systems that support big files.

    You can get more speed from the I/O bottleneck by putting RAID directories on different physical disks. The only allowed RAID_TYPE is STRIPED. 1 and RAID0 are aliases for STRIPED.

    If you specify the RAID_TYPE option for a MyISAM table, specify the RAID_CHUNKS and RAID_CHUNKSIZE options as well. The maximum RAID_CHUNKS value is 255. MyISAM creates RAID_CHUNKS subdirectories named 00, 01, 02, ... 09, 0a, 0b, ... in the database directory. In each of these directories, MyISAM creates a file tbl_name.MYD. When writing data to the data file, the RAID handler maps the first RAID_CHUNKSIZE*1024 bytes to the first file, the next RAID_CHUNKSIZE*1024 bytes to the next file, and so on.

    RAID_TYPE works on any operating system, as long as you have built MySQL with the --with-raid option to configure. To determine whether a server supports RAID tables, use SHOW VARIABLES LIKE 'have_raid' to see whether the variable value is YES.

  • ROW_FORMAT

    Defines how the rows should be stored. Currently, this option works only with 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 13.1.3, “MyISAM Table Storage Formats”.

    Note

    When executing a CREATE TABLE statement, if you specify a row format which 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.

  • 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 13.3, “The MERGE Storage Engine”.

    In MySQL 4.1, you must have SELECT, UPDATE, and DELETE privileges for the tables you map to a MERGE table.

    Note

    Originally, all tables used had to be in the same database as the MERGE table itself. This restriction has been lifted as of MySQL 4.1.1.

Important

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 allows 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.

As of MySQL 3.23, you can create one table from another by adding a SELECT statement at the end of the CREATE TABLE statement:

CREATE TABLE new_tbl SELECT * FROM orig_tbl;

MySQL creates new columns for all elements in the SELECT. For example:

mysql> CREATE TABLE test (a INT NOT NULL AUTO_INCREMENT,
    ->        PRIMARY KEY (a), KEY(b))
    ->        TYPE=MyISAM SELECT b,c FROM test2;

This creates a MyISAM table with three columns, a, b, and c. Notice that the columns from the SELECT statement are appended to the right side of the table, not overlapped onto it. Take the following example:

mysql> SELECT * FROM foo;
+---+
| n |
+---+
| 1 |
+---+

mysql> CREATE TABLE bar (m INT) SELECT n FROM foo;
Query OK, 1 row affected (0.02 sec)
Records: 1  Duplicates: 0  Warnings: 0

mysql> SELECT * FROM bar;
+------+---+
| m    | n |
+------+---+
| NULL | 1 |
+------+---+
1 row in set (0.00 sec)

For each row in table foo, a row is inserted in bar with the values from foo and default values for the new columns.

In a table resulting from CREATE TABLE ... SELECT, columns named only in the CREATE TABLE part come first. Columns named in both parts or only in the SELECT part come after that. The data type of SELECT columns can be overridden by also specifying the column in the CREATE TABLE part.

If any errors occur while copying the data to the table, it is automatically dropped and not created.

CREATE TABLE ... SELECT does not automatically create any indexes for you. This is done intentionally to make the statement as flexible as possible. If you want to have indexes in the created table, you should specify these before the SELECT statement:

mysql> CREATE TABLE bar (UNIQUE (n)) SELECT n FROM foo;

Some conversion of data types might occur. For example, the AUTO_INCREMENT attribute is not preserved, and VARCHAR columns can become CHAR columns. Retrained attributes are NULL (or NOT NULL) and, for those columns that have them, CHARACTER SET, COLLATION, COMMENT, and the DEFAULT clause.

When creating a table with CREATE ... SELECT, make sure to alias any function calls or expressions in the query. If you do not, the CREATE statement might fail or result in undesirable column names.

CREATE TABLE artists_and_works
  SELECT artist.name, COUNT(work.artist_id) AS number_of_works
  FROM artist LEFT JOIN work ON artist.id = work.artist_id
  GROUP BY artist.id;

As of MySQL 4.1, you can explicitly specify the data type for a generated column:

CREATE TABLE foo (a TINYINT NOT NULL) SELECT b+1 AS a FROM bar;

For CREATE TABLE ... SELECT, if IF NOT EXISTS is given and the table already exists, MySQL handles the statement as follows:

  • The table definition given in the CREATE TABLE part is ignored. No error occurs, even if the definition does not match that of the existing table.

  • If there is a mismatch between the number of columns in the table and the number of columns produced by the SELECT part, the selected values are assigned to the rightmost columns. For example, if the table contains n columns and the SELECT produces m columns, where m < n, the selected values are assigned to the m rightmost columns in the table. Each of the initial n – m columns is assigned its default value, either that specified explicitly in the column definition or the implicit column data type default if the definition contains no default. If the SELECT part produces too many columns (m > n), an error occurs.

The following example illustrates IF NOT EXISTS handling:

mysql> CREATE TABLE t1 (i1 INT DEFAULT 0, i2 INT, i3 INT, i4 INT);
Query OK, 0 rows affected (0.05 sec)

mysql> CREATE TABLE IF NOT EXISTS t1 (c1 CHAR(10)) SELECT 1, 2;
Query OK, 1 row affected, 1 warning (0.01 sec)
Records: 1  Duplicates: 0  Warnings: 0

mysql> SELECT * FROM t1;
+------+------+------+------+
| i1   | i2   | i3   | i4   |
+------+------+------+------+
|    0 | NULL |    1 |    2 |
+------+------+------+------+
1 row in set (0.00 sec)

In MySQL 4.1, you can also use LIKE to create an empty table based on the definition of another table, including any column attributes and indexes the original table has:

CREATE TABLE new_tbl LIKE orig_tbl;

The copy is created using the same version of the table storage format as the original table.

CREATE TABLE ... LIKE does not preserve any DATA DIRECTORY or INDEX DIRECTORY table options that were specified for the original table, or any foreign key definitions.

If the original table is a TEMPORARY table, CREATE TABLE ... LIKE does not preserve TEMPORARY. To create a TEMPORARY destination table, use CREATE TEMPORARY TABLE ... LIKE.

You can precede the SELECT by IGNORE or REPLACE to indicate how to handle rows that duplicate unique key values. With IGNORE, new rows that duplicate an existing row on a unique key value are discarded. With REPLACE, new rows replace rows that have the same unique key value. If neither IGNORE nor REPLACE is specified, duplicate unique key values result in an error.

To ensure that the update log or binary log can be used to re-create the original tables, MySQL does not allow concurrent inserts for CREATE TABLE ... SELECT statements.

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User Comments

Posted by Erik Sliman on May 24 2004 8:48am  

For 3.23.58 using InnoDB, I discovered that if you have a unique index key with multiple optional columns, then it does not apply a unique constraint at all if ANY of your data values for the columns are null. Thus, it will duplicate any data that has any nulls in any of the key columns.

If none of your column values are null, then it applies the unique constraint.

This was unexpected, because I remember Oracle applying the unique constraint on the remaining non-null values. It would be nice if MySQL could do this as well so we can guarantee that a unique key will not permit duplicates.

Posted by Martin Friebe on February 22 2005 6:04pm  

just found a possibility to wotrk around the limitations of not reopening temp tables (works in 4.1.10 , but wouldnt bet on its future);

create temporary table tmp1 (...);

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

# this will only work is the merge table is temporary itself

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

they are all temporary, so no clean up

Posted by Jeff Donner on August 11 2005 3:14am  

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 Ulrich Ulrich on May 25 2006 8:05am  

I just found a work around 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 Samba Pedapalli on January 2 2010 7:13am  

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`)
ON DELETE NO ACTION
ON UPDATE NO ACTION)
ENGINE = InnoDB
DEFAULT CHARACTER SET = utf8
COLLATE = utf8_bin