title: CHANGE COLUMN summary: TiDB 数据库中 CHANGE COLUMN 的使用概况。

CHANGE COLUMN

ALTER TABLE.. CHANGE COLUMN 语句用于在已有表上更改列，包括对列进行重命名，和将数据改为兼容类型。

语法图

  1. AlterTableStmt ::=
  2.     'ALTER' IgnoreOptional 'TABLE' TableName ( AlterTableSpecListOpt AlterTablePartitionOpt | 'ANALYZE' 'PARTITION' PartitionNameList ( 'INDEX' IndexNameList )? AnalyzeOptionListOpt )
  4. AlterTableSpec ::=
  5.     TableOptionList
  6. |   'SET' 'TIFLASH' 'REPLICA' LengthNum LocationLabelList
  7. |   'CONVERT' 'TO' CharsetKw ( CharsetName | 'DEFAULT' ) OptCollate
  8. |   'ADD' ( ColumnKeywordOpt IfNotExists ( ColumnDef ColumnPosition | '(' TableElementList ')' ) | Constraint | 'PARTITION' IfNotExists NoWriteToBinLogAliasOpt ( PartitionDefinitionListOpt | 'PARTITIONS' NUM ) )
  9. |   ( ( 'CHECK' | 'TRUNCATE' ) 'PARTITION' | ( 'OPTIMIZE' | 'REPAIR' | 'REBUILD' ) 'PARTITION' NoWriteToBinLogAliasOpt ) AllOrPartitionNameList
  10. |   'COALESCE' 'PARTITION' NoWriteToBinLogAliasOpt NUM
  11. |   'DROP' ( ColumnKeywordOpt IfExists ColumnName RestrictOrCascadeOpt | 'PRIMARY' 'KEY' | 'PARTITION' IfExists PartitionNameList | ( KeyOrIndex IfExists | 'CHECK' ) Identifier | 'FOREIGN' 'KEY' IfExists Symbol )
  12. |   'EXCHANGE' 'PARTITION' Identifier 'WITH' 'TABLE' TableName WithValidationOpt
  13. |   ( 'IMPORT' | 'DISCARD' ) ( 'PARTITION' AllOrPartitionNameList )? 'TABLESPACE'
  14. |   'REORGANIZE' 'PARTITION' NoWriteToBinLogAliasOpt ReorganizePartitionRuleOpt
  15. |   'ORDER' 'BY' AlterOrderItem ( ',' AlterOrderItem )*
  16. |   ( 'DISABLE' | 'ENABLE' ) 'KEYS'
  17. |   ( 'MODIFY' ColumnKeywordOpt IfExists | 'CHANGE' ColumnKeywordOpt IfExists ColumnName ) ColumnDef ColumnPosition
  18. |   'ALTER' ( ColumnKeywordOpt ColumnName ( 'SET' 'DEFAULT' ( SignedLiteral | '(' Expression ')' ) | 'DROP' 'DEFAULT' ) | 'CHECK' Identifier EnforcedOrNot | 'INDEX' Identifier IndexInvisible )
  19. |   'RENAME' ( ( 'COLUMN' | KeyOrIndex ) Identifier 'TO' Identifier | ( 'TO' | '='? | 'AS' ) TableName )
  20. |   LockClause
  21. |   AlgorithmClause
  22. |   'FORCE'
  23. |   ( 'WITH' | 'WITHOUT' ) 'VALIDATION'
  24. |   'SECONDARY_LOAD'
  25. |   'SECONDARY_UNLOAD'
  27. ColumnName ::=
  28.     Identifier ( '.' Identifier ( '.' Identifier )? )?
  30. ColumnDef ::=
  31.     ColumnName ( Type | 'SERIAL' ) ColumnOptionListOpt
  33. ColumnPosition ::=
  34.     ( 'FIRST' | 'AFTER' ColumnName )?

示例

  1. CREATE TABLE t1 (id int not null primary key AUTO_INCREMENT, col1 INT);
  1. Query OK, 0 rows affected (0.11 sec)
  1. INSERT INTO t1 (col1) VALUES (1),(2),(3),(4),(5);
  1. Query OK, 5 rows affected (0.02 sec)
  2. Records: 5  Duplicates: 0  Warnings: 0
  1. ALTER TABLE t1 CHANGE col1 col2 INT;
  1. Query OK, 0 rows affected (0.09 sec)
  1. ALTER TABLE t1 CHANGE col2 col3 BIGINT, ALGORITHM=INSTANT;
  1. Query OK, 0 rows affected (0.08 sec)
  1. ALTER TABLE t1 CHANGE col3 col3 INT;
  1. ERROR 1105 (HY000): unsupported modify column length 11 is less than origin 20
  1. ALTER TABLE t1 CHANGE col3 col3 BLOB;
  1. ERROR 1105 (HY000): unsupported modify column type 252 not match origin 8
  1. ALTER TABLE t1 CHANGE col3 col4 BIGINT, CHANGE id id2 INT NOT NULL;
  1. ERROR 1105 (HY000): can't run multi schema change

MySQL 兼容性

  • 不支持在单个 ALTER TABLE 语句中进行多个更改。
  • 不支持有损变更，比如从 BIGINT 变为 INTEGER，或者从 VARCHAR(255) 变为 VARCHAR(10)。
  • 不支持修改 DECIMAL 类型的精度。
  • 不支持更改 UNSIGNED 属性。

另请参阅