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

AlterTableStmt

DROP COLUMN - 图1

DropColumnSpec

DROP COLUMN - 图2

ColumnName

DROP COLUMN - 图3

1. AlterTableStmt
2. ::= 'ALTER' 'IGNORE'? 'TABLE' TableName DropColumnSpec ( ',' DropColumnSpec )*

4. DropColumnSpec
5. ::= 'DROP' 'COLUMN'? 'IF EXISTS'? ColumnName ( 'RESTRICT' | 'CASCADE' )?

7. ColumnName
8. ::= 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

  • 目前不支持删除主键列或组合索引相关列。

另请参阅