UPDATE

语法描述

UPDATE 用于修改表中的现有记录。

语法结构

单表语法结构

1. UPDATE table_reference
2. SET assignment_list
3. [WHERE where_condition]
4. [ORDER BY ...]
5. [LIMIT row_count]

参数释义

  • UPDATE 将新值更新到指定表中现有行的列中。
  • SET 从句指出要修改哪些列以及它们应该被赋予的值。每个值可以作为表达式给出，或者通过 DEFAULT 明确将列设置为默认值。
  • WHERE 从句，用于指定用于标识要更新哪些行的条件。若无 WHERE 从句，则更新所有行。
  • ORDER BY 从句，指按照指定的顺序更新行。
  • LIMIT 从句用于限制可更新的行数。

示例

  • 单表示例
1. CREATE TABLE t1 (a bigint(3), b bigint(5) primary key);
2. insert INTO t1 VALUES (1,1),(1,2);
3. update t1 set a=2 where a=1 limit 1;

5. mysql> select * from t1;
6. +------+------+
7. | a    | b    |
8. +------+------+
9. |    2 |    1 |
10. |    1 |    2 |
11. +------+------+
  • 多表示例
1. drop table if exists t1;
2. create table t1 (a int);
3. insert into t1 values(1), (2), (4);
4. drop table if exists t2;
5. create table t2 (b int);
6. insert into t2 values(1), (2), (3);
7. update t1, t2 set a = 1, b =2;

9. mysql> select * from t1;
10. +------+
11. | a    |
12. +------+
13. |    1 |
14. |    1 |
15. |    1 |
16. +------+

18. update t1, t2 set a = null, b =null;

20. mysql> select * from t2;
21. +------+
22. | b    |
23. +------+
24. | NULL |
25. | NULL |
26. | NULL |
27. +------+
28. mysql> select * from t1;
29. +------+
30. | a    |
31. +------+
32. | NULL |
33. | NULL |
34. | NULL |
35. +------+

支持多表 JOIN 语句。

1. drop table if exists t1;
2. drop table if exists t2;
3. create table t1 (a int, b int, c int);
4. insert into t1 values(1, 2, 3), (4, 5, 6), (7, 8, 9);
5. create table t2 (a int, b int, c int);
6. insert into t2 values(1, 2, 3), (4, 5, 6), (7, 8, 9);
7. update t1 join t2 on t1.a = t2.a set t1.b = 222, t1.c = 333, t2.b = 222, t2.c = 333;

9. mysql> select * from t1;
10. +------+------+------+
11. | a    | b    | c    |
12. +------+------+------+
13. |    1 |  222 |  333 |
14. |    4 |  222 |  333 |
15. |    7 |  222 |  333 |
16. +------+------+------+

18. mysql> with t11 as (select * from (select * from t1) as t22) update t11 join t2 on t11.a = t2.a set t2.b = 666;

20. mysql> select * from t2;
21. +------+------+------+
22. | a    | b    | c    |
23. +------+------+------+
24. |    1 |  666 |  333 |
25. |    4 |  666 |  333 |
26. |    7 |  666 |  333 |
27. +------+------+------+
28. 3 rows in set (0.00 sec)