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

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 )? )?

Examples

  1. mysql> CREATE TABLE t1 (id INT NOT NULL PRIMARY KEY AUTO_INCREMENT, col1 INT NOT NULL, col2 INT NOT NULL);
  2. Query OK, 0 rows affected (0.12 sec)
  4. mysql> INSERT INTO t1 (col1,col2) VALUES (1,1),(2,2),(3,3),(4,4),(5,5);
  5. Query OK, 5 rows affected (0.02 sec)
  6. Records: 5  Duplicates: 0  Warnings: 0
  8. mysql> SELECT * FROM t1;
  9. +----+------+------+
  10. | id | col1 | col2 |
  11. +----+------+------+
  12. |  1 |    1 |    1 |
  13. |  2 |    2 |    2 |
  14. |  3 |    3 |    3 |
  15. |  4 |    4 |    4 |
  16. |  5 |    5 |    5 |
  17. +----+------+------+
  18. 5 rows in set (0.01 sec)
  20. mysql> ALTER TABLE t1 DROP COLUMN col1, DROP COLUMN col2;
  21. ERROR 1105 (HY000): can't run multi schema change
  22. mysql> SELECT * FROM t1;
  23. +----+------+------+
  24. | id | col1 | col2 |
  25. +----+------+------+
  26. |  1 |    1 |    1 |
  27. |  2 |    2 |    2 |
  28. |  3 |    3 |    3 |
  29. |  4 |    4 |    4 |
  30. |  5 |    5 |    5 |
  31. +----+------+------+
  32. 5 rows in set (0.00 sec)
  34. mysql> ALTER TABLE t1 DROP COLUMN col1;
  35. Query OK, 0 rows affected (0.27 sec)
  37. mysql> SELECT * FROM t1;
  38. +----+------+
  39. | id | col2 |
  40. +----+------+
  41. |  1 |    1 |
  42. |  2 |    2 |
  43. |  3 |    3 |
  44. |  4 |    4 |
  45. |  5 |    5 |
  46. +----+------+
  47. 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