MySQL 中两个 select 之间的区别?
mysqlmysqli database
您可以使用子查询来计算 MySQL 中两个 select 之间的区别。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) -> ); Query OK, 0 rows affected (0.87 sec)
使用 insert 命令在表中插入一些记录。 查询语句如下:
mysql> insert into DifferenceSelectDemo(UserId,UserValue) values(10,10); Query OK, 1 row affected (0.24 sec) mysql> insert into DifferenceSelectDemo(UserId,UserValue) values(10,20); Query OK, 1 row affected (0.15 sec) mysql> insert into DifferenceSelectDemo(UserId,UserValue) values(20,30); Query OK, 1 row affected (0.17 sec) mysql> insert into DifferenceSelectDemo(UserId,UserValue) values(20,20); Query OK, 1 row affected (0.19 sec) mysql> insert into DifferenceSelectDemo(UserId,UserValue) values(30,40); Query OK, 1 row affected (0.14 sec) mysql> insert into DifferenceSelectDemo(UserId,UserValue) values(30,20); Query OK, 1 row affected (0.15 sec)
使用 select 语句显示表中的所有记录。查询如下:
mysql> select *from DifferenceSelectDemo;
输出结果如下:
+----+--------+-----------+ | 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)
以下是获取两个选择之间的差异的查询:
mysql> select *from DifferenceSelectDemo -> WHERE UserValue NOT IN (select UserValue from DifferenceSelectDemo where Id=1);
输出结果如下:
+----+--------+-----------+ | 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)
