CHANGE COLUMN
The ALTER TABLE.. CHANGE COLUMN statement changes a column on an existing table. The change can include both renaming the column, and changing the data type to a compatible type.
Synopsis
- AlterTableStmt
- AlterTableSpec
- ColumnName
- ColumnDef
- ColumnPosition
AlterTableStmt ::=
'ALTER' IgnoreOptional 'TABLE' TableName ( AlterTableSpecListOpt AlterTablePartitionOpt | 'ANALYZE' 'PARTITION' PartitionNameList ( 'INDEX' IndexNameList )? AnalyzeOptionListOpt )
AlterTableSpec ::=
TableOptionList
| 'SET' 'TIFLASH' 'REPLICA' LengthNum LocationLabelList
| 'CONVERT' 'TO' CharsetKw ( CharsetName | 'DEFAULT' ) OptCollate
| 'ADD' ( ColumnKeywordOpt IfNotExists ( ColumnDef ColumnPosition | '(' TableElementList ')' ) | Constraint | 'PARTITION' IfNotExists NoWriteToBinLogAliasOpt ( PartitionDefinitionListOpt | 'PARTITIONS' NUM ) )
| ( ( 'CHECK' | 'TRUNCATE' ) 'PARTITION' | ( 'OPTIMIZE' | 'REPAIR' | 'REBUILD' ) 'PARTITION' NoWriteToBinLogAliasOpt ) AllOrPartitionNameList
| 'COALESCE' 'PARTITION' NoWriteToBinLogAliasOpt NUM
| 'DROP' ( ColumnKeywordOpt IfExists ColumnName RestrictOrCascadeOpt | 'PRIMARY' 'KEY' | 'PARTITION' IfExists PartitionNameList | ( KeyOrIndex IfExists | 'CHECK' ) Identifier | 'FOREIGN' 'KEY' IfExists Symbol )
| 'EXCHANGE' 'PARTITION' Identifier 'WITH' 'TABLE' TableName WithValidationOpt
| ( 'IMPORT' | 'DISCARD' ) ( 'PARTITION' AllOrPartitionNameList )? 'TABLESPACE'
| 'REORGANIZE' 'PARTITION' NoWriteToBinLogAliasOpt ReorganizePartitionRuleOpt
| 'ORDER' 'BY' AlterOrderItem ( ',' AlterOrderItem )*
| ( 'DISABLE' | 'ENABLE' ) 'KEYS'
| ( 'MODIFY' ColumnKeywordOpt IfExists | 'CHANGE' ColumnKeywordOpt IfExists ColumnName ) ColumnDef ColumnPosition
| 'ALTER' ( ColumnKeywordOpt ColumnName ( 'SET' 'DEFAULT' ( SignedLiteral | '(' Expression ')' ) | 'DROP' 'DEFAULT' ) | 'CHECK' Identifier EnforcedOrNot | 'INDEX' Identifier IndexInvisible )
| 'RENAME' ( ( 'COLUMN' | KeyOrIndex ) Identifier 'TO' Identifier | ( 'TO' | '='? | 'AS' ) TableName )
| LockClause
| AlgorithmClause
| 'FORCE'
| ( 'WITH' | 'WITHOUT' ) 'VALIDATION'
| 'SECONDARY_LOAD'
| 'SECONDARY_UNLOAD'
ColumnName ::=
Identifier ( '.' Identifier ( '.' Identifier )? )?
ColumnDef ::=
ColumnName ( Type | 'SERIAL' ) ColumnOptionListOpt
ColumnPosition ::=
( 'FIRST' | 'AFTER' ColumnName )?
Examples
mysql> CREATE TABLE t1 (id int not null primary key AUTO_INCREMENT, col1 INT);
Query OK, 0 rows affected (0.11 sec)
mysql> INSERT INTO t1 (col1) VALUES (1),(2),(3),(4),(5);
Query OK, 5 rows affected (0.02 sec)
Records: 5 Duplicates: 0 Warnings: 0
mysql>
mysql> ALTER TABLE t1 CHANGE col1 col2 INT;
Query OK, 0 rows affected (0.09 sec)
mysql> ALTER TABLE t1 CHANGE col2 col3 BIGINT, ALGORITHM=INSTANT;
Query OK, 0 rows affected (0.08 sec)
mysql>
mysql> ALTER TABLE t1 CHANGE col3 col3 INT;
ERROR 1105 (HY000): unsupported modify column length 11 is less than origin 20
mysql> ALTER TABLE t1 CHANGE col3 col3 BLOB;
ERROR 1105 (HY000): unsupported modify column type 252 not match origin 8
mysql> ALTER TABLE t1 CHANGE col3 col4 BIGINT, CHANGE id id2 INT NOT NULL;
ERROR 1105 (HY000): can't run multi schema change
MySQL compatibility
- Making multiple changes in a single
ALTER TABLEstatement is not currently supported. - Only certain types of data type changes are supported. For example, an
INTEGERtoBIGINTis supported, but the reverse is not possible. Changing from an integer to a string format or blob is not supported. - Modifying precision of the
DECIMALtype is not supported. - Changing the
UNSIGNEDattribute is not supported.