UPDATE 
===========================



描述 
-----------

该语句用于修改表中的字段值。

格式 
-----------

```javascript
UPDATE [IGNORE] table_references
    SET update_asgn_list
    [WHERE where_condition] 
    [ORDER BY order_list]
    [LIMIT row_count];

table_references:
    tbl_name [PARTITION (partition_name,...)] [, ...]

update_asgn_list:
    column_name = expr [, ...]

order_list: 
    column_name [ASC|DESC] [, column_name [ASC|DESC]...]
```



参数解释 
-------------



|      **参数**      |           **描述**            |
|------------------|-----------------------------|
| IGNORE           | 在 INSERT 语句执行过程中发生的错误将会被忽略。 |
| table_references | 指定修改表名，多表修改时，表名直接'，'作为间隔。   |
| where_condition  | 指定过滤条件。                     |
| row_count        | 限制的行数。                      |
| tbl_name         | 插入表名。                       |
| partition_name   | 插入表指定的分区名。                  |
| column_name      | 列名。                         |
| column_name ASC  | 按列名升序修改。                    |
| column_name DESC | 按列名降序修改。                    |



注意事项 
-------------

不管是多表还是单表更新都不支持直接对子查询进行更新值操作，例如：`update (select * from t1) set c1 = 100;`

示例 
-----------

1. 创建示例表 t1 和 t2。




```javascript
OceanBase(admin@test)>create table t1(c1 int primary key, c2 int);
Query OK, 0 rows affected (0.16 sec)
OceanBase(admin@test)>select * from t1;
+----+------+
| c1 | c2   |
+----+------+
|  1 |    1 |
|  2 |    2 |
|  3 |    3 |
|  4 |    4 |
+----+------+
4 rows in set (0.06 sec)

OceanBase(admin@test)>create table t2(c1 int primary key, c2 int) partition by key(c1) partitions 4;
Query OK, 0 rows affected (0.19 sec)
OceanBase(admin@test)>select * from t2;
+----+------+
| c1 | c2   |
+----+------+
|  5 |    5 |
|  1 |    1 |
|  2 |    2 |
|  3 |    3 |
+----+------+
4 rows in set (0.02 sec)
```



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




```javascript
OceanBase(admin@test)>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

OceanBase(admin@test)>select * from t1;
+----+------+
| c1 | c2   |
+----+------+
|  1 |  100 |
|  2 |    2 |
|  3 |    3 |
|  4 |    4 |
+----+------+
4 rows in set (0.01 sec)
```



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




```javascript
OceanBase(admin@test)>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

OceanBase(admin@test)>select * from t1;
+----+------+
| c1 | c2   |
+----+------+
|  1 |  100 |
|  2 |  100 |
|  3 |    3 |
|  4 |    4 |
+----+------+
4 rows in set (0.01 sec)
```



4. 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。




```javascript
OceanBase(admin@test)>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

OceanBase(admin@test)>select * from t2;
+----+------+
| c1 | c2   |
+----+------+
|  5 |    5 |
|  1 |    1 |
|  2 |    2 |
|  3 |  100 |
+----+------+
4 rows in set (0.06 sec)
```



5. 修改多个表。将 t1 表和 t2 表中满足 "t1.c1 = t2.c1" 对应行的数据 t1 表中的 c2 列值修改为 100，t2 表中的 c2 列值修改为 200。




```javascript
OceanBase(admin@test)>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

OceanBase(admin@test)>select * from t1;
+----+------+
| c1 | c2   |
+----+------+
|  1 |  100 |
|  2 |  100 |
|  3 |  100 |
|  4 |    4 |
+----+------+
4 rows in set (0.00 sec)

OceanBase(admin@test)>select * from t2;
+----+------+
| c1 | c2   |
+----+------+
|  5 |    5 |
|  1 |  200 |
|  2 |  200 |
|  3 |  200 |
+----+------+
4 rows in set (0.01 sec)
```



6. 修改多个表。修改 t1 表和 t2 表的p2分区中满足 "t1.c1 = t2.c1" 对应行的数据 t1 表中的 c2 列值修改为 100，t2 表中的 c2 列值修改为 200。




```javascript
OceanBase(admin@test)>update t1,t2 partition(p2) set t1.c2 = 100, t2.c2 = 200 where t1.c2 = t2.c2;
Query OK, 6 rows affected (0.02 sec)
Rows matched: 6  Changed: 6  Warnings: 0

OceanBase(admin@test)>select * from t1;
+----+------+
| c1 | c2   |
+----+------+
|  1 |  100 |
|  2 |  100 |
|  3 |  100 |
|  4 |    4 |
+----+------+
4 rows in set (0.01 sec)

OceanBase(admin@test)>select * from t2;
+----+------+
| c1 | c2   |
+----+------+
|  5 |    5 |
|  1 |  200 |
|  2 |  200 |
|  3 |  200 |
+----+------+
4 rows in set (0.01 sec)
```



7. 对可更新视图 v 进行更新值。




```javascript
OceanBase(admin@test)>create view v as select * from t1;
Query OK, 0 rows affected (0.07 sec)

OceanBase(admin@test)>update v set v.c2 = 100 where v.c1 = 1;
Query OK, 1 row affected (0.02 sec)
Rows matched: 1  Changed: 1  Warnings: 0

OceanBase(admin@test)>select * from v;
+----+------+
| c1 | c2   |
+----+------+
|  1 |  100 |
|  2 |    2 |
|  3 |    3 |
|  4 |    4 |
+----+------+
4 rows in set (0.01 sec)
```



