mysql中的NULL的判断

最新推荐文章于 2025-08-09 20:21:24 发布

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最新推荐文章于 2025-08-09 20:21:24 发布

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文章标签：数据库

原文链接：http://www.cnblogs.com/justinzhang/p/4780102.html

本文介绍了在MySQL中如何正确地删除包含NULL值的记录。通过对比不同的SQL语句，解释了为什么不能直接使用'delete where x = NULL'，并给出了正确的解决方案：使用'where x is null'。

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mysql> delete from `zhangchao` where x='NULL';

Query OK, 0 rows affected (0.00 sec)

mysql> delete from `zhangchao` where x=NULL; 
Query OK, 0 rows affected (0.00 sec)

mysql> select * from zhangchao;
+------+-------+
| x    | y     |
+------+-------+
| xxx  | yyy   |
| NULL | NULL  |
| xxx  | james |
| xxx  | lucy  |
| xxx  | alex  |
+------+-------+
5 rows in set (0.00 sec)

mysql> delete from `zhangchao` where x  is null;
Query OK, 1 row affected (0.00 sec)

mysql> select * from zhangchao;
+------+-------+
| x    | y     |
+------+-------+
| xxx  | yyy   |
| xxx  | james |
| xxx  | lucy  |
| xxx  | alex  |
+------+-------+
4 rows in set (0.00 sec)

mysql>