黑马视频-子查询

子查询：独立子查询 相关子查询select * from (select col1,col2 from Tbl) as Tb

1、一个查询结果作为另一个查询的数据源 ,必须将子查询数据源 别名 as Tbs

select * from (select fname ,fage,fgender from MyStudent where fage between 18 and 25 and fgender='女') as Tbswhere fname like '%赵'

2、作为列

select 最高分= select max(score) from Tbs, 最低分=select min(score) from Tbs,
平均分=select avg(score) from Tbs

3、将查询结果作为查询条件

select * from TblStudent where tsclassid=(select tsclassid form TblClass where className ='高二二班')
4、子查询只能返回单个值 select * from Tbls where classId in (select classId from Tbs where classId='4' or classId='5')5、exists中包含的查询查到了结果则exists返回true，否则为falseelse
select * from Tbl where exists( select * from Tbl1 where name='高二二班' and Tbl.classId=Tbl1.classId)
select * ,row_number() over (order by fid desc) as number from tb
20页，每页5条select * from ( select *,row_number() over (order by fid dsc ) as number from Tb
)as TbNew where tbNew.number between 19*5+1 and 20*5
row_number() 行号
select * ,count(*) from Tbl （错误）select * ,count(*) over () as 总条数 from Tbl

来自为知笔记(Wiz)