更新数据 
=========================

使用 `UPDATE` 语句修改表中的字段值。

示例如下：

创建示例表 `t1` 和 `t2`。

```sql
obclient> CREATE TABLE t1(c1 int primary key, c2 int);
Query OK, 0 rows affected (0.16 sec)
obclient> INSERT t1 VALUES(1,1),(2,2),(3,3),(4,4);
Query OK, 4 rows affected (0.02 sec)
Records: 4  Duplicates: 0  Warnings: 0
obclient> SELECT * FROM t1;
+----+------+
| c1 | c2   |
+----+------+
|  1 |    1 |
|  2 |    2 |
|  3 |    3 |
|  4 |    4 |
+----+------+
4 rows in set (0.06 sec)

obclient> CREATE TABLE t2(c1 int primary key, c2 int) partition by key(c1) partitions 4;
Query OK, 0 rows affected(0.19 sec)
obclient> INSERT t2 VALUES(5,5),(1,1),(2,2),(3,3);
Query OK, 4 rows affected (0.01 sec)
Records: 4  Duplicates: 0  Warnings: 0
obclient> SELECT * FROM t2;
+----+------+
| c1 | c2   |
+----+------+
|  5 |    5 |
|  1 |    1 |
|  2 |    2 |
|  3 |    3 |
+----+------+
4 rows in set (0.02 sec)
```



* 将表 `t1` 中 `t1.c1=1` 对应的那一行数据的 `c2` 列值修改为 `100`。

  ```sql
  obclient> UPDATE t1 SET t1.c2 = 100 WHERE t1.c1 = 1;
  Query OK, 1 row affected (0.02 sec)
  Rows matched: 1  Changed: 1  Warnings: 0
  
  obclient> SELECT * FROM t1;
  +----+------+
  | c1 | c2   |
  +----+------+
  |  1 |  100 |
  |  2 |    2 |
  |  3 |    3 |
  |  4 |    4 |
  +----+------+
  4 rows in set (0.01 sec)
  ```

  

* 将表 `t1` 中按照 `c2` 列排序的前两行数据的 `c2` 列值修改为 `100`。

  ```sql
  obclient> UPDATE t1 set t1.c2 = 100 ORDER BY c2 LIMIT 2;
  Query OK, 2 rows affected (0.02 sec)
  Rows matched: 2  Changed: 2  Warnings: 0
  
  obclient> SELECT * FROM t1;
  +----+------+
  | c1 | c2   |
  +----+------+
  |  1 |  100 |
  |  2 |  100 |
  |  3 |    3 |
  |  4 |    4 |
  +----+------+
  4 rows in set (0.01 sec)
  ```

  

* 将表 `t2` 中 `p2` 分区的数据中 `t2.c1 > 2` 的对应行数据的 `c2` 列值修改为 `100`。

  ```sql
  obclient> SELECT * FROM t2 partition (p2);
  +----+------+
  | c1 | c2   |
  +----+------+
  |  1 |    1 |
  |  2 |    2 |
  |  3 |    3 |
  +----+------+
  3 rows in set (0.01 sec)
  
  obclient> UPDATE t2 partition(p2) SET t2.c2 = 100 WHERE t2.c1 > 2;
  Query OK, 1 row affected (0.02 sec)
  Rows matched: 1  Changed: 1  Warnings: 0
  
  obclient> SELECT * FROM t2 partition (p2);
  +----+------+
  | c1 | c2   |
  +----+------+
  |  1 |    1 |
  |  2 |    2 |
  |  3 |  100 |
  +----+------+
  3 rows in set (0.00 sec)
  ```

  

* 修改多个表。对于表 `t1` 和表 `t2` 中满足 `t1.c2 = t2.c2` 对应行的数据，将表 `t1` 中的 `c2` 列值修改为 `100`，表 `t2` 中的 `c2` 列值修改为 `200`。

  ```sql
  obclient> UPDATE t1,t2 SET t1.c2 = 100, t2.c2 = 200 WHERE t1.c2 = t2.c2;
  Query OK, 6 rows affected (0.03 sec)
  Rows matched: 6  Changed: 6  Warnings: 0
  
  obclient> SELECT * FROM t1;
  +----+------+
  | c1 | c2   |
  +----+------+
  |  1 |  100 |
  |  2 |  100 |
  |  3 |  100 |
  |  4 |    4 |
  +----+------+
  4 rows in set (0.00 sec)
  
  obclient> SELECT * FROM t2;
  +----+------+
  | c1 | c2   |
  +----+------+
  |  5 |    5 |
  |  1 |  200 |
  |  2 |  200 |
  |  3 |  200 |
  +----+------+
  4 rows in set (0.01 sec)
  ```

  




更多 `UPDATE` 语句相关的语法请参见《SQL 参考（MySQL 模式）》中 [UPDATE](../../10.sql-reference/5.sql-statement/61.UPDATE.md)章节。
