在 MySQL 中为单个列实现两个条件，分别为 null 和空值
mysqlmysqli database更新于 2025/10/18 14:04:17
首先我们创建一个表 −
mysql> create table DemoTable635( EmployeId int NOT NULL AUTO_INCREMENT PRIMARY KEY,EmployeeName varchar(100) ); Query OK, 0 rows affected (1.24 sec)
使用 insert 命令在表中插入一些记录 −
mysql> insert into DemoTable635(EmployeeName) values('John');
Query OK, 1 row affected (0.20 sec)
mysql> insert into DemoTable635(EmployeeName) values('Sam');
Query OK, 1 row affected (0.27 sec)
mysql> insert into DemoTable635(EmployeeName) values('');
Query OK, 1 row affected (0.38 sec)
mysql> insert into DemoTable635(EmployeeName) values(null);
Query OK, 1 row affected (0.12 sec)
mysql> insert into DemoTable635(EmployeeName) values('David');
Query OK, 1 row affected (0.22 sec)
使用 select 语句显示表中的所有记录 −
mysql> select *from DemoTable635;
这将产生以下输出 −
+-----------+--------------+ | EmployeId | EmployeeName | +-----------+--------------+ | 1 | John | | 2 | Sam | | 3 | | | 4 | NULL | | 5 | David | +-----------+--------------+ 5 rows in set (0.00 sec)
以下查询是为了避免显示 MySQL 列中的空值和 Null 值 −
mysql> select *from DemoTable635 tbl where tbl.EmployeeName is not null and tbl.EmployeeName <> '';
这将产生以下输出 −
+-----------+--------------+ | EmployeId | EmployeeName | +-----------+--------------+ | 1 | John | | 2 | Sam | | 5 | David | +-----------+--------------+ 3 rows in set (0.02 sec)
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