《Mysql入门MySQL查询空字段或非空字段(is null和not null)》要点: 本文介绍了Mysql入门MySQL查询空字段或非空字段(is null和not null),希望对您有用。如果有疑问,可以联系我们。
MYSQL实例现在我们先来把test表中的一条记录的birth字段设置为空.
mysql> update test set t_birth=null where t_id=1;
Query OK,1 row affected (0.02 sec)
Rows matched: 1? Changed: 1? Warnings: 0
OK,执行成功!
设置一个字段值为空时的语法为:set <字段名>=NULL
说明一下,这里没有大小写的区分,可以是null,也可以是NULL.
下面看看结果:
mysql> select * from test;
+------+--------+----------------------------------+------------+
| t_id | t_name | t_password?????????????????????? | t_birth??? |
+------+--------+----------------------------------+------------+
|??? 1 | name1? | 12345678901234567890123456789012 | NULL?????? |
|??? 2 | name2? | 12345678901234567890123456789012 | 2013-01-01 |
+------+--------+----------------------------------+------------+
2 rows in set (0.00 sec)
接下来分别查询一下字段t_birth值为空或不为空的记录:
mysql> select * from test where t_birth is null;
+------+--------+----------------------------------+---------+
| t_id | t_name | t_password?????????????????????? | t_birth |
+------+--------+----------------------------------+---------+
|??? 1 | name1? | 12345678901234567890123456789012 | NULL??? |
+------+--------+----------------------------------+---------+
1 row in set (0.00 sec)
mysql> select * from test where t_birth is not null;
+------+--------+----------------------------------+------------+
| t_id | t_name | t_password?????????????????????? | t_birth??? |
+------+--------+----------------------------------+------------+
|??? 2 | name2? | 12345678901234567890123456789012 | 2013-01-01 |
+------+--------+----------------------------------+------------+
1 row in set (0.00 sec)
说明:
1、查询字段值为空的语法:where <字段名> is null
2、查询字段值不为空的语法:where <字段名> is not null
关于MySQL查询空字段或非空字段(is null和not null),本文就介绍这么多,希望对大家有所帮助,谢谢!? 编程之家PHP培训学院每天发布《Mysql入门MySQL查询空字段或非空字段(is null和not null)》等实战技能,PHP、MYSQL、LINUX、APP、JS,CSS全面培养人才。 (编辑:李大同)
【声明】本站内容均来自网络,其相关言论仅代表作者个人观点,不代表本站立场。若无意侵犯到您的权利,请及时与联系站长删除相关内容!
|