ALTER TABLE

ALTER TABLE 语句用于对已有表进行修改，以符合新表结构。ALTER TABLE 语句可用于：

语法图

AlterTableStmt:

AlterTableStmt

TableName:

TableName

AlterTableSpec:

AlterTableSpec

示例

  1. mysql> CREATE TABLE t1 (id INT NOT NULL PRIMARY KEY auto_increment, c1 INT NOT NULL);
  2. Query OK, 0 rows affected (0.11 sec)
  4. mysql> INSERT INTO t1 (c1) VALUES (1),(2),(3),(4),(5);
  5. Query OK, 5 rows affected (0.03 sec)
  6. Records: 5  Duplicates: 0  Warnings: 0
  8. mysql> EXPLAIN SELECT * FROM t1 WHERE c1 = 3;
  9. +---------------------+----------+------+-------------------------------------------------------------+
  10. | id                  | count    | task | operator info                                               |
  11. +---------------------+----------+------+-------------------------------------------------------------+
  12. | TableReader_7       | 10.00    | root | data:Selection_6                                            |
  13. | └─Selection_6       | 10.00    | cop  | eq(test.t1.c1, 3)                                           |
  14. |   └─TableScan_5     | 10000.00 | cop  | table:t1, range:[-inf,+inf], keep order:false, stats:pseudo |
  15. +---------------------+----------+------+-------------------------------------------------------------+
  16. 3 rows in set (0.00 sec)
  18. mysql> ALTER TABLE t1 ADD INDEX (c1);
  19. Query OK, 0 rows affected (0.30 sec)
  21. mysql> EXPLAIN SELECT * FROM t1 WHERE c1 = 3;
  22. +-------------------+-------+------+-----------------------------------------------------------------+
  23. | id                | count | task | operator info                                                   |
  24. +-------------------+-------+------+-----------------------------------------------------------------+
  25. | IndexReader_6     | 10.00 | root | index:IndexScan_5                                               |
  26. | └─IndexScan_5     | 10.00 | cop  | table:t1, index:c1, range:[3,3], keep order:false, stats:pseudo |
  27. +-------------------+-------+------+-----------------------------------------------------------------+
  28. 2 rows in set (0.00 sec)

MySQL 兼容性

  • 支持除空间类型外的所有数据类型。
  • 不支持 FULLTEXT，HASH 和 SPATIAL 索引。

另请参阅