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一个sql问题研究

发表于: 2013-11-30   作者:asialee   来源:转载   浏览:
摘要:             假设有下面的数据表:               create table test ( ID` bigint(20) NOT NULL AUTO_INCREMENT, NAME varchar(20) not null, HO

            假设有下面的数据表: 

            

create table test (
ID` bigint(20) NOT NULL AUTO_INCREMENT,
NAME varchar(20) not null, HOBBY varchar(20) not null);  
 insert into test values('Adam','basketball');
 insert into test values('Bill','basketball');
 insert into test values('Bill','football');
 insert into test values('Cyper','basketball');
 insert into test values('Cyper','badminton');
 insert into test values('David','basketball');
 insert into test values('David','badminton');
 insert into test values('David','table tennis');

 

    用SQL语句查出哪些人即会玩basketball又会玩badminton,找出这样的name组合,即输出:

   Cyper,David. 我想到了用下面的一些方法:

  •  使用最简单的方式,这个里面由于使用了group by,个人感觉不需要加distinct
select name FROM TEST 
WHERE hobby in ('basketball','badminton') 
group by name having count(name) = 2;

 

 

  • 使用比较简单的in子查询来实现,需要加distinct
select distinct(name)
from Test
where name in (
          select name from Test
          where hobby in('basketball','badminton')
          group by name 
          having count(name) = 2
);

 

 

 

  •  使用子查询,个人感觉此处不需要加distinct
select from Test a
WHERE hobby = 'basketball'
AND EXISTS (SELECT * from TEST_test b
WHERE a.name = b.name AND b.hobby = 'badminton');

 

 

  •  使用复杂的子查询,但是效率不敢恭维
select distinct(name) from Test as t1
where exists (
    select 1 from Test as t2
    where t2.name = t1.name and hobby = 'basketball')
and exists (
    select 1 from Test as t3
     where t3.name = t1.name and hobby = 'badminton'
);

 

 

  •  使用表联合查询
select distinct(t1.name)
from Test t1,Test t2,Test t3
where t1.name = t2.name and t1.name = t3.name and 
t2.hobby = 'basketball' and t3.hobby = 'badminton';

 

 

  •  根据题目的要求进行枚举分析
select t1.* from Test t1, Test t2 where t1.name=t2.name 
and( 
t1.hobby='basketball' and t2.hobby='badminton' or 
t2.hobby='basketball' and t1.hobby='badminton' 
)

 

 

 

 

 

一个sql问题研究

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