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

DropColumnSpec

ColumnName

AlterTableStmt
         ::= 'ALTER' 'IGNORE'? 'TABLE' TableName DropColumnSpec ( ',' DropColumnSpec )*
DropColumnSpec
         ::= 'DROP' 'COLUMN'? 'IF EXISTS'? ColumnName ( 'RESTRICT' | 'CASCADE' )?
ColumnName
         ::= Identifier ( '.' Identifier ( '.' Identifier )? )?

示例

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

Query OK, 0 rows affected (0.12 sec)

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

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

SELECT * FROM t1;

+----+------+------+
| id | col1 | col2 |
+----+------+------+
|  1 |    1 |    1 |
|  2 |    2 |    2 |
|  3 |    3 |    3 |
|  4 |    4 |    4 |
|  5 |    5 |    5 |
+----+------+------+
5 rows in set (0.01 sec)

ALTER TABLE t1 DROP COLUMN col1, DROP COLUMN col2;

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

SELECT * FROM t1;

+----+------+------+
| id | col1 | col2 |
+----+------+------+
|  1 |    1 |    1 |
|  2 |    2 |    2 |
|  3 |    3 |    3 |
|  4 |    4 |    4 |
|  5 |    5 |    5 |
+----+------+------+
5 rows in set (0.00 sec)

ALTER TABLE t1 DROP COLUMN col1;

Query OK, 0 rows affected (0.27 sec)

SELECT * FROM t1;

+----+------+
| id | col2 |
+----+------+
|  1 |    1 |
|  2 |    2 |
|  3 |    3 |
|  4 |    4 |
|  5 |    5 |
+----+------+
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

• ADD COLUMN
• SHOW CREATE TABLE
• CREATE TABLE