mysql——多表——子查询——示例

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子查询:

子查询是将一个查询语句嵌套在另外一个查询语句中,内层查询语句的查询结果,可以作为外来层查询语句提供查询条件。

因此在特定条件下,一个查询语句的条件,需要另外一个查询语句来获取。

前期准备表:

create table employee ( num int(50),
                        d_id int(50),
                        name varchar(50),
                        age int(50),
                        sex varchar(50),
                        homeadd varchar(50)
                       );

insert into employee values(1,1001,\'zhangsan\',26,\'nan\',\'beijing\'); insert into employee values(2,1001,\'lisi\',24,\'nv\',\'hunan\'); insert into employee values(3,1002,\'wangwu\',25,\'nan\',\'jiangsu\'); insert into employee values(4,1004,\'aric\',15,\'nan\',\'yingguo\');

select * from employee;





create table department ( d_id int(50), d_name varchar(50), functione varchar(50), address varchar(50) );

insert into department values(1001,\'keyanbu\',\'yanfachanpin\',\'3lou5hao\'); insert into department values(1002,\'shengchanbu\',\'shengchanchanp\',\'5louyiceng\'); insert into department values(1003,\'xiaoshoubu\',\'cehuaxiaoshou\',\'1louxiaoshoudating\');


select * from department;

 

一、带in关键字的子查询

select * from employee where d_id in (select d_id from department );

 

 

 

select * from employee where d_id not in (select d_id from department );

 

 

 

 

二、带exists关键字的子查询

exists关键字表示存在,使用exists关键字时,内层查询语句不用返回查询的记录。而是返回一个真假值。

如果内层查询语句查询到满足条件的记录,就返回一个真值(true);否则,返回一个假值(false);

当返回值为true时,外层查询语句将进行查询;而返回false时,外层查询语句不进行查询或者查询不出任何记录。

select * from employee where exists (select d_name from department where d_id = 1003);

 

 

 

 

select * from employee where exists (select d_name from department where d_id = 1004);

 

 

 

其它:

exists关键字可以与其他查询条件一起使用。条件表达式与exists关键字之间用and或者or来连接。

select * from employee where age > 24 and exists (select d_name from department where d_id = 1003);

select * from employee where age > 24 and exists (select d_name from department where d_id = 1004);


not exists与exists相反。

select * from employee where age > 24 and not exists (select d_name from department where d_id = 1003);

select * from employee where age > 24 and not exists (select d_name from department where d_id = 1004);

 

 

===================================================================

 

准备语句:

create table schoarship ( levela int(50),
                          score int(50)
                         );

insert into schoarship(levela,score) values(1,90); insert into schoarship values(2,80); insert into schoarship values(3,70);
select * from schoarship;


create table computer_stu ( id int(50), name varchar(50), score int(50) );
insert into computer_stu(id,name,score) values (1001,\'lily\',85); insert into computer_stu(id,name,score) values (1002,\'tom\',91), (1003,\'jim\',87), (1004,\'aric\',77), (1005,\'lucy\',65), (1006,\'andy\',99), (1007,\'ada\',85), (1008,\'jeck\',70);
select * from computer_stu;

 

select * from schoarship;

 

 

select * from computer_stu;

 

 

 

 

3、带比较运算符的子查询

select id,name,score from computer_stu where score >= (select score from schoarship where levela = 1);

/* 查询获得一等奖学金的学生有哪些,第一个表为奖学金等级和最低分数*/

 

 

 

select d_id,d_name from department where d_id != (select d_id from employee where age = 24);

/*只有生产部和销售部没有年龄等于24岁的员工*/

 

 

 

 

 

4、带any关键字的子查询


any关键字表示满足其中任何一个条件。使用any关键字时,只要满足内查询语句返回的结果中的任何一个,就可以通过该条件来执行外层查询语句

 

select * from computer_stu where score >= any ( select score from schoarship );

/*结果显示,有7个人获得奖学金,只有id为1005的人没有,因为分数为65,不高于奖学金指定最低分数的任何一个*/

 

 

 

 

 

 

5、带all关键字的子查询

all关键字表示满足所有条件。使用all关键字时,只有满足内层查询语句返回的所有结果,才可以执行外层查询语句。

 

select * from computer_stu where score >= all ( select score from schoarship );

/*结果显示,只有两个人获得奖学金。因为这两个人的分数比所有奖学金要求的分数都高*/

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