Question

如何根据以前的值更新mysql中的字段？

让我们说count等于3。

UPDATE MY_TABLE SET count = count-1

那会有用吗？所以count的新值将是4

Answer 1

你的意思是排还是桌子？如果您的意思是插入或更新一行，您可以使用triggers。

Answer 2

我试了一下它有用，所以也许你需要向我们展示表的CREATE语句。测试结果：

mysql> create table aint ( count int not null default 0 );
Query OK, 0 rows affected (0.25 sec)

mysql> insert into aint VALUES(1);
Query OK, 1 row affected (0.06 sec)

mysql> select * from aint;
+-------+
| count |
+-------+
|     1 |
+-------+
1 row in set (0.00 sec)

mysql> update aint set count = count-1;
Query OK, 1 row affected (0.06 sec)
Rows matched: 1  Changed: 1  Warnings: 0

mysql> select * from aint;
+-------+
| count |
+-------+
|     0 |
+-------+
1 row in set (0.00 sec)

mysql> update aint set count = count-1;
Query OK, 1 row affected (0.00 sec)
Rows matched: 1  Changed: 1  Warnings: 0

mysql> select * from aint;
+-------+
| count |
+-------+
|    -1 |
+-------+
1 row in set (0.00 sec)

mysql根据字段值更新行

2 个答案: