sql数据分组最大值,第一条,前三条方法总结,三个实例都比较简单都是根据GROUP BY出来的数据进行一些简单操作即可,有需要的同学可参考一下.
取分组前三第记录
代码如下 | 复制代码 |
SELECT 课程, |
取分组第一第记录
例
表Demo的数据都是字符串类型,按照顺序的时间Time(也是字符串)排序的记录如下:
Num Name Time
1 a 2009/05/01
1 a 2009/05/02
1 a 2009/05/03
2 b 2009/05/04
2 b 2009/05/05
3 c 2009/05/06
3 c 2009/05/07
5 e 2009/05/08
1 a 2009/05/09
1 a 2009/05/10
我想输出类似按照Num分组的每组的第一条数据记录,比如上面的记录我想操作后得到如下记录:
Num Name Time
1 a 2009/05/01
2 b 2009/05/04
3 c 2009/05/06
5 e 2009/05/08
1 a 2009/05/09
sql代码
代码如下 | 复制代码 |
declare @Tab table select * from @Tab t where not exists(select 1 from @Tab where num=t.num and [time] /* (4 行受影响) |
取分组最大记录
示例:test 表 a b c
1 5 abc
2 6 bcd
1 7 ade
2 8 adc
若取按a列分组后,b列最大,的所有列的记录:
result a b c
1 6 bcd
2 8 adc
可以使用如下语句:
代码如下 | 复制代码 |
select * from test where b in (select max(id) from test group by a) 适用于所有数据库: select t1.a,t1.b,t1.c from test t1 inner join (seelct a,max(b) as b from test group by a) t2 on t1.a=t2.a and t1.b=t2.b 适用于所有数据库: select a,b,c from( select a,b,c ,row_number()over(partition by a order by b desc) rn from test ) where rn=1 |

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monacoeditor创建//创建和设置值if(!this.monacoEditor){this.monacoEditor=monaco.editor.create(this._node,{value:value||code,language:language,...options});this.monacoEditor.onDidChangeModelContent(e=>{constvalue=this.monacoEditor.getValue();//使value和其值保持一致i

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monacoeditor创建//创建和设置值if(!this.monacoEditor){this.monacoEditor=monaco.editor.create(this._node,{value:value||code,language:language,...options});this.monacoEditor.onDidChangeModelContent(e=>{constvalue=this.monacoEditor.getValue();//使value和其值保持一致i

0x01前言概述小编又在MySQL中发现了一个Double型数据溢出。当我们拿到MySQL里的函数时,小编比较感兴趣的是其中的数学函数,它们也应该包含一些数据类型来保存数值。所以小编就跑去测试看哪些函数会出现溢出错误。然后小编发现,当传递一个大于709的值时,函数exp()就会引起一个溢出错误。mysql>selectexp(709);+-----------------------+|exp(709)|+-----------------------+|8.218407461554972


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