UPDATE

UPDATE 语句用于修改指定表中的数据。

语法图

UpdateStmt

UPDATE - 图1

UpdateOption

UPDATE - 图2

TableRef

UPDATE - 图3

TableRefs

UPDATE - 图4

1. UpdateStmt ::=
2. "UPDATE" UpdateOption
3. (   TableRef "SET" Assignment ("," Assignment)* WhereClause? OrderBy? Limit?
4. |   TableRefs "SET" Assignment ("," Assignment)* WhereClause?
5. )

7. UpdateOption ::=
8. OptimizerHints? ("LOW_PRIORITY" | "HIGH_PRIORITY" | "DELAYED")? "IGNORE"?

10. TableRef ::=
11. ( TableFactor | JoinTable )

13. TableRefs ::=
14. EscapedTableRef ("," EscapedTableRef)*

示例

1. CREATE TABLE t1 (id INT NOT NULL PRIMARY KEY AUTO_INCREMENT, c1 INT NOT NULL);

1. Query OK, 0 rows affected (0.11 sec)

1. INSERT INTO t1 (c1) VALUES (1), (2), (3);

1. Query OK, 3 rows affected (0.02 sec)
2. Records: 3  Duplicates: 0  Warnings: 0

1. SELECT * FROM t1;

1. +----+----+
2. | id | c1 |
3. +----+----+
4. |  1 |  1 |
5. |  2 |  2 |
6. |  3 |  3 |
7. +----+----+
8. 3 rows in set (0.00 sec)

1. UPDATE t1 SET c1=5 WHERE c1=3;

1. Query OK, 1 row affected (0.01 sec)
2. Rows matched: 1  Changed: 1  Warnings: 0

1. SELECT * FROM t1;

1. +----+----+
2. | id | c1 |
3. +----+----+
4. |  1 |  1 |
5. |  2 |  2 |
6. |  3 |  5 |
7. +----+----+
8. 3 rows in set (0.00 sec)

MySQL 兼容性

在计算表达式中的列时，TiDB 总使用原始的值。例如：

1. CREATE TABLE t (a int, b int);
2. INSERT INTO t VALUES (1,2);
3. UPDATE t SET a = a+1,b=a;

在 MySQL 中，b 列的值会被更新成 2，因为 b 列被设置为与 a 列相同，而 a（最初是 1）在同一条语句中被更新成了 2。

TiDB 遵守标准的 SQL 行为，这里将 b 列值更新成 1。

另请参阅