MySQL中两个选择之间的区别？
您可以使用子查询来区分MySQL中的两个选择。语法如下：
SELECT *FROM yourTableName where yourColumnName NOT IN(SELECT yourColumnName FROM youTableName WHERE yourCondition;
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 DifferenceSelectDemo -> ( -> Id int NOT NULL AUTO_INCREMENT, -> UserId int, -> UserValue int, -> PRIMARY KEY(Id) -> );
使用insert命令在表中插入一些记录。查询如下：
mysql> insert into DifferenceSelectDemo(UserId,UserValue) values(10,10); mysql> insert into DifferenceSelectDemo(UserId,UserValue) values(10,20); mysql> insert into DifferenceSelectDemo(UserId,UserValue) values(20,30); mysql> insert into DifferenceSelectDemo(UserId,UserValue) values(20,20); mysql> insert into DifferenceSelectDemo(UserId,UserValue) values(30,40); mysql> insert into DifferenceSelectDemo(UserId,UserValue) values(30,20);
使用select语句显示表中的所有记录。查询如下：
mysql> select *from DifferenceSelectDemo;
以下是输出：
+----+--------+-----------+ | Id | UserId | UserValue | +----+--------+-----------+ | 1 | 10 | 10 | | 2 | 10 | 20 | | 3 | 20 | 30 | | 4 | 20 | 20 | | 5 | 30 | 40 | | 6 | 30 | 20 | +----+--------+-----------+ 6 rows in set (0.02 sec)
这是获取两个选择之间差异的查询：
mysql> select *from DifferenceSelectDemo -> WHERE UserValue NOT IN (select UserValue from DifferenceSelectDemo where Id=1);
以下是输出：
+----+--------+-----------+ | Id | UserId | UserValue | +----+--------+-----------+ | 2 | 10 | 20 | | 3 | 20 | 30 | | 4 | 20 | 20 | | 5 | 30 | 40 | | 6 | 30 | 20 | +----+--------+-----------+ 5 rows in set (0.09 sec)