mysql分組取最大(最小、最新、前N條)條記錄

在數據庫開發過程當中，咱們要爲每種類型的數據取出前幾條記錄，或者是取最新、最小、最大等等，這個該如何實現呢，本文章向你們介紹如何實現mysql分組取最大(最小、最新、前N條)條記錄。須要的能夠參考一下。

先看一下本示例中須要使用到的數據

建立表並插入數據：

insert into tb values('a',    2,   'a2');
insert into tb values('a',    1,   'a1');
insert into tb values('a',    3,   'a3');
insert into tb values('b',    1,   'b1');
insert into tb values('b',    3,   'b3');
insert into tb values('b',    2,   'b2');
insert into tb values('b',    4,   'b4');
insert into tb values('b',    5,   'b5');

數據表以下：

name	val	memo
a	2	a2
a	1	a1
a	3	a3
b	1	b1
b	3	b3
b	2	b2
b	4	b4
b	5	b5

按name分組取val最大的值所在行的數據

方法一：

select a.* from tb a where val = (select max(val) from tb where name = a.name) order by a.name

方法二：

select a.* from tb a where not exists(select 1 from tb where name = a.name and val > a.val)

方法三：

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

方法四：

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

方法五：

select a.* from tb a where 1 > (select count(*) from tb where name = a.name and val > a.val ) order by a.name

方法六:

select * from (select * from tb ORDER BY val desc) temp GROUP BY name ORDER BY val desc;

以上六種方法運行的結果均爲以下所示：

name	val	memo
a	3	a3
b	5	b5

小編推薦使用第1、第3、第四鍾方法,結果顯示第1,3,4種方法效率相同，第2，5種方法效率差些。

按name分組取val最小的值所在行的數據

方法一：

select a.* from tb a where val = (select min(val) from tb where name = a.name) order by a.name

方法二：

select a.* from tb a where not exists(select 1 from tb where name = a.name and val < a.val)

方法三：

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

方法四：

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

方法五：

select a.* from tb a where 1 > (select count(*) from tb where name = a.name and val < a.val) order by a.name

以上五種方法運行的結果均爲以下所示：

name	val	memo
a	1	a1
b	1	b1

按name分組取第一次出現的行所在的數據 

sql以下：

select a.* from tb a where val = (select top 1 val from tb where name = a.name) order by a.name
//這個是sql server的
//mysql應該是
select a.* from tb a where val = (select val from tb where name = a.name limit 1) order by a.name

結果以下：

name	val	memo
a	2	a2
b	1	b1

按name分組取最小的兩個(N個)val

第一種方法：

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

第二種方法：

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

第三種方法：

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

結果以下：

name	val	memo
a	1	a1
a	2	a2
b	1	b1
b	2	b2

按name分組取最大的兩個(N個)val

第一種方法：

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

第二種方法：

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

第三種方法：

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

結果以下：

name	val	memo
a	3	a3
a	2	a2
b	5	b5
b	4	b4