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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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