mysql分組取最大(最小、最新、前N條)條記錄
在數據庫開發過程中,我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,本文章向大家介紹如何實現mysql分組取最大(最小、最新、前N條)條記錄。需要的可以參考一下。
先看一下本示例中需要使用到的數據
創建表並插入數據:
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');
數據表如下:
namevalmemoa2a2a1a1a3a3b1b1b3b3b2b2b4b4b5b5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如下所示:
namevalmemoa3a3b5b5
小編推薦使用第一、第三、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如下所示:
namevalmemoa1a1b1b1按name分組取第一次出現的行所在的數據
sql如下:
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
結果如下:
namevalmemoa2a2b1b1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
結果如下:
namevalmemoa1a1a2a2b1b1b2b2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
結果如下:
namevalmemoa3a3a2a2b5b5b4b4
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