1.分別求出孫悟空、豬八戒、沙僧的總打怪數select sum(kills) from user1 a join user_kills b on a.id=b.user_id where a.user_name='孫悟空' ;
select sum(kills) from user1 a join user_kills b on a.id=b.user_id where a.user_name='豬八戒' ;
select sum(kills) from user1 a join user_kills b on a.id=b.user_id where a.user_name='沙僧' ;
2.是從cross join的方式關聯上述3個表的結果select * from
(select sum(kills) as '孫悟空' from user1 a join user_kills b on a.id=b.user_id where a.user_name='孫悟空' ) a
cross join
(select sum(kills) as '豬八戒' from user1 a join user_kills b on a.id=b.user_id where a.user_name='豬八戒') b
cross join
(select sum(kills) as '沙僧' from user1 a join user_kills b on a.id=b.user_id where a.user_name='沙僧') c
select * from
(select sum(hour) as '張三' from teachers a join teacherdate b on a.name=b.name where a.name='張三' ) a
cross join
(select sum(hour) as '李四' from teachers a join teacherdate b on a.name=b.name where a.name='李四') b
cross join
(select sum(hour) as '王五' from teachers a join teacherdate b on a.name=b.name where a.name='王五') c
3.使用case的方式實現select
sum(case when b.name='張三' then b.hour end) as '張三',
sum(case when b.name='李四' then b.hour end) as '李四',
sum(case when b.name='王五' then b.hour end) as '王五'
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