DROP COLUMN

DROP COLUMN 语句用于从指定的表中删除列。在 TiDB 中，COLUMN 为在线操作，不会阻塞表中的数据读写。

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 )? )?

示例

1. CREATE TABLE t1 (id INT NOT NULL PRIMARY KEY AUTO_INCREMENT, col1 INT NOT NULL, col2 INT NOT NULL);

1. Query OK, 0 rows affected (0.12 sec)

1. INSERT INTO t1 (col1,col2) VALUES (1,1),(2,2),(3,3),(4,4),(5,5);

1. Query OK, 5 rows affected (0.02 sec)
2. Records: 5  Duplicates: 0  Warnings: 0

1. SELECT * FROM t1;

1. +----+------+------+
2. | id | col1 | col2 |
3. +----+------+------+
4. |  1 |    1 |    1 |
5. |  2 |    2 |    2 |
6. |  3 |    3 |    3 |
7. |  4 |    4 |    4 |
8. |  5 |    5 |    5 |
9. +----+------+------+
10. 5 rows in set (0.01 sec)

1. ALTER TABLE t1 DROP COLUMN col1, DROP COLUMN col2;

1. ERROR 1105 (HY000): can't run multi schema change

1. SELECT * FROM t1;

1. +----+------+------+
2. | id | col1 | col2 |
3. +----+------+------+
4. |  1 |    1 |    1 |
5. |  2 |    2 |    2 |
6. |  3 |    3 |    3 |
7. |  4 |    4 |    4 |
8. |  5 |    5 |    5 |
9. +----+------+------+
10. 5 rows in set (0.00 sec)

1. ALTER TABLE t1 DROP COLUMN col1;

1. Query OK, 0 rows affected (0.27 sec)

1. SELECT * FROM t1;

1. +----+------+
2. | id | col2 |
3. +----+------+
4. |  1 |    1 |
5. |  2 |    2 |
6. |  3 |    3 |
7. |  4 |    4 |
8. |  5 |    5 |
9. +----+------+
10. 5 rows in set (0.00 sec)

MySQL 兼容性

  • 目前不支持在一条语句中同时删除多个列。
  • 目前不支持删除主键列或组合索引相关列。

另请参阅