MySQL 中是否存在 NOT EQUAL?
mysqlmysqli database
是的，MySQL 中 <> 运算符的形式存在 NOT EQUAL。语法如下 −
SELECT * FROM yourTableName WHERE yourColumnName <> yourValue;
为了理解上述语法，让我们创建一个表。创建表的查询如下−
mysql> create table DoesNotEqualDemo -> ( -> Id int NOT NULL AUTO_INCREMENT, -> Name varchar(20), -> PRIMARY KEY(Id) -> ); Query OK, 0 rows affected (0.98 sec)
使用 insert 命令在表中插入一些记录。插入记录的查询如下−
mysql> insert into DoesNotEqualDemo(Name) values(NULL);
Query OK, 1 row affected (0.24 sec)
mysql> insert into DoesNotEqualDemo(Name) values('John');
Query OK, 1 row affected (0.18 sec)
mysql> insert into DoesNotEqualDemo(Name) values('Carol');
Query OK, 1 row affected (0.43 sec)
mysql> insert into DoesNotEqualDemo(Name) values('Bob');
Query OK, 1 row affected (0.13 sec)
mysql> insert into DoesNotEqualDemo(Name) values('');
Query OK, 1 row affected (0.13 sec)
mysql> insert into DoesNotEqualDemo(Name) values('Larry');
Query OK, 1 row affected (0.13 sec)
mysql> insert into DoesNotEqualDemo(Name) values(NULL);
Query OK, 1 row affected (0.10 sec)
使用 select 语句显示表中的所有记录。查询如下−
mysql> select *from DoesNotEqualDemo;
以下是输出 −
+----+-------+ | Id | Name | +----+-------+ | 1 | NULL | | 2 | John | | 3 | Carol | | 4 | Bob | | 5 | | | 6 | Larry | | 7 | NULL | +----+-------+ 7 rows in set (0.00 sec)
以下查询用于选择所有不等于 NULL 以及空字符串的记录 −
mysql> select *from DoesNotEqualDemo where Name <> 'NULL' and Name <> '';
以下是输出 −
+----+-------+ | Id | Name | +----+-------+ | 2 | John | | 3 | Carol | | 4 | Bob | | 6 | Larry | +----+-------+ 4 rows in set (0.00 sec)
