一个简单的Update语句-优快云博客

本文通过一个具体实例演示了如何使用MySQL的UPDATE语句来更新表中的数据。示例中，使用了一个子查询从一个表（aa）中选择等级（grade），然后用这个值更新另一个表（bb）中的年龄（age）。这一操作展示了如何跨表更新数据。

一个简单的Update语句

mysql> create table aa(name varchar(100),grade int(5));
Query OK, 0 rows affected (0.09 sec)

mysql> create table bb(name varchar(100),age int(5));
Query OK, 0 rows affected (0.14 sec)

mysql> insert into aa values('AAA',80);
Query OK, 1 row affected (0.05 sec)

mysql> insert into aa values('BBB',60);
Query OK, 1 row affected (0.06 sec)

mysql> insert into aa values('CCC',60);
Query OK, 1 row affected (0.03 sec)

mysql> insert into bb values('CCC',26);
Query OK, 1 row affected (0.05 sec)

mysql> insert into bb values('BBB',24);
Query OK, 1 row affected (0.03 sec)

mysql> insert into bb values('AAA',26);
Query OK, 1 row affected (0.03 sec)

mysql> select * from aa;
+------+-------+
| name | grade |
+------+-------+
| AAA |    80 |
| BBB |    60 |
| CCC |    60 |
+------+-------+
3 rows in set (0.00 sec)

mysql> select * from bb;
+------+------+
| name | age |
+------+------+
| CCC |   26 |
| BBB |   24 |
| AAA |   26 |
+------+------+
3 rows in set (0.00 sec)

--用aa表的grade更新bb表的age

mysql> update bb b set age=(select grade from aa a where a.name=b.name);
Query OK, 3 rows affected (0.03 sec)
Rows matched: 3 Changed: 3 Warnings: 0

mysql> select * from bb;
+------+------+
| name | age |
+------+------+
| CCC |   60 |
| BBB |   60 |
| AAA |   80 |
+------+------+
3 rows in set (0.00 sec)

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