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sql-statement-update.md

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UPDATE
TiDB 数据库中 UPDATE 的使用概况。
/docs-cn/dev/sql-statements/sql-statement-update/
/docs-cn/dev/reference/sql/statements/update/

UPDATE

UPDATE 语句用于修改指定表中的数据。

语法图

UpdateStmt ::=
    "UPDATE" UpdateOption
(   TableRef "SET" Assignment ("," Assignment)* WhereClause? OrderBy? Limit?
|   TableRefs "SET" Assignment ("," Assignment)* WhereClause?
)

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

TableRef ::=
    ( TableFactor | JoinTable )

TableRefs ::=
    EscapedTableRef ("," EscapedTableRef)*

示例

{{< copyable "sql" >}}

CREATE TABLE t1 (id INT NOT NULL PRIMARY KEY AUTO_INCREMENT, c1 INT NOT NULL);
Query OK, 0 rows affected (0.11 sec)

{{< copyable "sql" >}}

INSERT INTO t1 (c1) VALUES (1), (2), (3);
Query OK, 3 rows affected (0.02 sec)
Records: 3  Duplicates: 0  Warnings: 0

{{< copyable "sql" >}}

SELECT * FROM t1;
+----+----+
| id | c1 |
+----+----+
|  1 |  1 |
|  2 |  2 |
|  3 |  3 |
+----+----+
3 rows in set (0.00 sec)

{{< copyable "sql" >}}

UPDATE t1 SET c1=5 WHERE c1=3;
Query OK, 1 row affected (0.01 sec)
Rows matched: 1  Changed: 1  Warnings: 0

{{< copyable "sql" >}}

SELECT * FROM t1;
+----+----+
| id | c1 |
+----+----+
|  1 |  1 |
|  2 |  2 |
|  3 |  5 |
+----+----+
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：

CREATE TABLE t (a int, b int);
INSERT INTO t VALUES (1,2);
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