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DROP COLUMN

此语句用于从指定的表中删除列。TiDB 中的 DROP COLUMN 支持在线操作,意味着它不会阻塞读写操作。

概要

AlterTableStmt
ALTERIGNORETABLETableNameDropColumnSpec,
DropColumnSpec
DROPCOLUMNIF EXISTSColumnNameRESTRICTCASCADE
ColumnName
Identifier.Identifier.Identifier

示例

mysql> 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) mysql> 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 mysql> 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) mysql> ALTER TABLE t1 DROP COLUMN col1, DROP COLUMN col2; ERROR 1105 (HY000): can't run multi schema change mysql> 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) mysql> ALTER TABLE t1 DROP COLUMN col1; Query OK, 0 rows affected (0.27 sec) mysql> 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

  • 不支持删除主键列或被复合索引覆盖的列。

相关链接

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