mysql 非空语法_MySQL查询空字段或非空字段(is null和not null)_MySQL

MySQL查询空字段或非空字段(is null和not null)_MySQL

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 =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 is null

2、查询字段值不为空的语法：where is not null

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