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DROP COLUMN

This statement drops a column from a specified table. DROP COLUMN is online in TiDB, which means that it does not block read or write operations.

Synopsis

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

Examples

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 compatibility

  • Dropping primary key columns or columns covered by the composite index is not supported.

See also

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