declare @t table(rq varchar(10),hh int,ye dec(6,2))
insert into @t select '2006-01-02' ,1111 ,2.01
union all select '2006-01-05' ,1111 ,3.51
union all select '2006-01-10' ,1111 ,2.55
union all select '2006-01-02' ,2222 ,3.00
union all select '2006-01-04' ,2222 ,2.00
union all select '2006-01-05' ,3333 ,6.54
union all select '2006-01-06' ,3333 ,5.23
union all select '2006-01-07' ,3333 ,8.55 select * from @t a where not exists(select 1 from @t where hh=a.hh and rq> a.rq) 结果:
2006-01-10 1111 2.55
2006-01-04 2222 2.00
2006-01-07 3333 8.55结果我明白,但不太明白这句是怎么执行的
select * from @t a where not exists(select 1 from @t where hh=a.hh and rq> a.rq)
insert into @t select '2006-01-02' ,1111 ,2.01
union all select '2006-01-05' ,1111 ,3.51
union all select '2006-01-10' ,1111 ,2.55
union all select '2006-01-02' ,2222 ,3.00
union all select '2006-01-04' ,2222 ,2.00
union all select '2006-01-05' ,3333 ,6.54
union all select '2006-01-06' ,3333 ,5.23
union all select '2006-01-07' ,3333 ,8.55 select * from @t a where not exists(select 1 from @t where hh=a.hh and rq> a.rq) 结果:
2006-01-10 1111 2.55
2006-01-04 2222 2.00
2006-01-07 3333 8.55结果我明白,但不太明白这句是怎么执行的
select * from @t a where not exists(select 1 from @t where hh=a.hh and rq> a.rq)
其实就是一个表作为两个表进行比较
(爱新觉罗.毓华 2007-10-23于浙江杭州)
/*
数据如下:
name val memo
a 2 a2(a的第二个值)
a 1 a1--a的第一个值
a 3 a3:a的第三个值
b 1 b1--b的第一个值
b 3 b3:b的第三个值
b 2 b2b2b2b2
b 4 b4b4
b 5 b5b5b5b5b5
*/
--创建表并插入数据:
create table tb(name varchar(10),val int,memo varchar(20))
insert into tb values('a', 2, 'a2(a的第二个值)')
insert into tb values('a', 1, 'a1--a的第一个值')
insert into tb values('a', 3, 'a3:a的第三个值')
insert into tb values('b', 1, 'b1--b的第一个值')
insert into tb values('b', 3, 'b3:b的第三个值')
insert into tb values('b', 2, 'b2b2b2b2')
insert into tb values('b', 4, 'b4b4')
insert into tb values('b', 5, 'b5b5b5b5b5')
go--一、按name分组取val最大的值所在行的数据。
--方法1:
select a.* from tb a where val = (select max(val) from tb where name = a.name) order by a.name
--方法2:
select a.* from tb a where not exists(select 1 from tb where name = a.name and val > a.val)
--方法3:
select a.* from tb a,(select name,max(val) val from tb group by name) b where a.name = b.name and a.val = b.val order by a.name
--方法4:
select a.* from tb a inner join (select name , max(val) val from tb group by name) b on a.name = b.name and a.val = b.val order by a.name
--方法5
select a.* from tb a where 1 > (select count(*) from tb where name = a.name and val > a.val ) order by a.name
/*
name val memo
---------- ----------- --------------------
a 3 a3:a的第三个值
b 5 b5b5b5b5b5
*/--二、按name分组取val最小的值所在行的数据。
--方法1:
select a.* from tb a where val = (select min(val) from tb where name = a.name) order by a.name
--方法2:
select a.* from tb a where not exists(select 1 from tb where name = a.name and val < a.val)
--方法3:
select a.* from tb a,(select name,min(val) val from tb group by name) b where a.name = b.name and a.val = b.val order by a.name
--方法4:
select a.* from tb a inner join (select name , min(val) val from tb group by name) b on a.name = b.name and a.val = b.val order by a.name
--方法5
select a.* from tb a where 1 > (select count(*) from tb where name = a.name and val < a.val) order by a.name
/*
name val memo
---------- ----------- --------------------
a 1 a1--a的第一个值
b 1 b1--b的第一个值
*/--三、按name分组取第一次出现的行所在的数据。
select a.* from tb a where val = (select top 1 val from tb where name = a.name) order by a.name
/*
name val memo
---------- ----------- --------------------
a 2 a2(a的第二个值)
b 1 b1--b的第一个值
*/--四、按name分组随机取一条数据。
select a.* from tb a where val = (select top 1 val from tb where name = a.name order by newid()) order by a.name
/*
name val memo
---------- ----------- --------------------
a 1 a1--a的第一个值
b 5 b5b5b5b5b5
*/--五、按name分组取最小的两个(N个)val
select a.* from tb a where 2 > (select count(*) from tb where name = a.name and val < a.val ) order by a.name,a.val
select a.* from tb a where val in (select top 2 val from tb where name=a.name order by val) order by a.name,a.val
select a.* from tb a where exists (select count(*) from tb where name = a.name and val < a.val having Count(*) < 2) order by a.name
/*
name val memo
---------- ----------- --------------------
a 1 a1--a的第一个值
a 2 a2(a的第二个值)
b 1 b1--b的第一个值
b 2 b2b2b2b2
*/--六、按name分组取最大的两个(N个)val
select a.* from tb a where 2 > (select count(*) from tb where name = a.name and val > a.val ) order by a.name,a.val
select a.* from tb a where val in (select top 2 val from tb where name=a.name order by val desc) order by a.name,a.val
select a.* from tb a where exists (select count(*) from tb where name = a.name and val > a.val having Count(*) < 2) order by a.name
/*
name val memo
---------- ----------- --------------------
a 2 a2(a的第二个值)
a 3 a3:a的第三个值
b 4 b4b4
b 5 b5b5b5b5b5
*/
--七,如果整行数据有重复,所有的列都相同。
/*
数据如下:
name val memo
a 2 a2(a的第二个值)
a 1 a1--a的第一个值
a 1 a1--a的第一个值
a 3 a3:a的第三个值
a 3 a3:a的第三个值
b 1 b1--b的第一个值
b 3 b3:b的第三个值
b 2 b2b2b2b2
b 4 b4b4
b 5 b5b5b5b5b5
*/
--在sql server 2000中只能用一个临时表来解决,生成一个自增列,先对val取最大或最小,然后再通过自增列来取数据。
--创建表并插入数据:
create table tb(name varchar(10),val int,memo varchar(20))
insert into tb values('a', 2, 'a2(a的第二个值)')
insert into tb values('a', 1, 'a1--a的第一个值')
insert into tb values('a', 1, 'a1--a的第一个值')
insert into tb values('a', 3, 'a3:a的第三个值')
insert into tb values('a', 3, 'a3:a的第三个值')
insert into tb values('b', 1, 'b1--b的第一个值')
insert into tb values('b', 3, 'b3:b的第三个值')
insert into tb values('b', 2, 'b2b2b2b2')
insert into tb values('b', 4, 'b4b4')
insert into tb values('b', 5, 'b5b5b5b5b5')
goselect * , px = identity(int,1,1) into tmp from tbselect m.name,m.val,m.memo from
(
select t.* from tmp t where val = (select min(val) from tmp where name = t.name)
) m where px = (select min(px) from
(
select t.* from tmp t where val = (select min(val) from tmp where name = t.name)
) n where n.name = m.name)drop table tb,tmp/*
name val memo
---------- ----------- --------------------
a 1 a1--a的第一个值
b 1 b1--b的第一个值(2 行受影响)
*/
--在sql server 2005中可以使用row_number函数,不需要使用临时表。
--创建表并插入数据:
create table tb(name varchar(10),val int,memo varchar(20))
insert into tb values('a', 2, 'a2(a的第二个值)')
insert into tb values('a', 1, 'a1--a的第一个值')
insert into tb values('a', 1, 'a1--a的第一个值')
insert into tb values('a', 3, 'a3:a的第三个值')
insert into tb values('a', 3, 'a3:a的第三个值')
insert into tb values('b', 1, 'b1--b的第一个值')
insert into tb values('b', 3, 'b3:b的第三个值')
insert into tb values('b', 2, 'b2b2b2b2')
insert into tb values('b', 4, 'b4b4')
insert into tb values('b', 5, 'b5b5b5b5b5')
goselect m.name,m.val,m.memo from
(
select * , px = row_number() over(order by name , val) from tb
) m where px = (select min(px) from
(
select * , px = row_number() over(order by name , val) from tb
) n where n.name = m.name)drop table tb/*
name val memo
---------- ----------- --------------------
a 1 a1--a的第一个值
b 1 b1--b的第一个值(2 行受影响)
*/
insert into @t select '2006-01-02' ,1111 ,2.01
union all select '2006-01-05' ,1111 ,3.51
union all select '2006-01-10' ,1111 ,2.55
union all select '2006-01-02' ,2222 ,3.00
union all select '2006-01-04' ,2222 ,2.00
union all select '2006-01-05' ,3333 ,6.54
union all select '2006-01-06' ,3333 ,5.23
union all select '2006-01-07' ,3333 ,8.55 --方法1:
select a.* from @t a where rq = (select min(rq) from @t where hh = a.hh) order by a.hh
--方法2:
select a.* from @t a where not exists(select 1 from @t where hh = a.hh and rq > a.rq)
--方法3:
select a.* from @t a,(select hh,max(rq) rq from @t group by hh) b where a.hh = b.hh and a.rq = b.rq order by a.hh
--方法4:
select a.* from @t a inner join (select hh , max(rq) rq from @t group by hh) b on a.hh = b.hh and a.rq = b.rq order by a.hh
--方法5
select a.* from @t a where 1 > (select count(*) from @t where hh = a.hh and rq > a.rq) order by a.hh/*
rq hh ye
---------- ----------- --------
2006-01-02 1111 2.01
2006-01-02 2222 3.00
2006-01-05 3333 6.54(所影响的行数为 3 行)rq hh ye
---------- ----------- --------
2006-01-10 1111 2.55
2006-01-04 2222 2.00
2006-01-07 3333 8.55(所影响的行数为 3 行)rq hh ye
---------- ----------- --------
2006-01-10 1111 2.55
2006-01-04 2222 2.00
2006-01-07 3333 8.55(所影响的行数为 3 行)rq hh ye
---------- ----------- --------
2006-01-10 1111 2.55
2006-01-04 2222 2.00
2006-01-07 3333 8.55(所影响的行数为 3 行)rq hh ye
---------- ----------- --------
2006-01-10 1111 2.55
2006-01-04 2222 2.00
2006-01-07 3333 8.55(所影响的行数为 3 行)*/