[sql server、oracle] 分組取最大值最小值常用sql

 sqlserver2005前：

--分組取最大最小常用sql
--測試環境
if OBJECT_ID('tb') is not null drop table tb;
go
create table tb(
 col1 int,
 col2 int,
 Fcount int)
insert into tb
select 11,20,1 union all
select 11,22,1 union all
select 11,23,2 union all
select 11,24,5 union all
select 12,39,1 union all
select 12,40,3 union all
select 12,38,4
go
--查詢
--1
select * from tb t where Fcount=(select max(Fcount)from tb where col1=t.col1)
--2
select * from tb t where not exists(select 1 from tb where col1=t.col1 and Fcount>t.Fcount)    --效率要高很多（lui2015-5-13注釋）
--結果
/*
col1        col2        Fcount
----------- ----------- -----------
12          38          4
11          24          5

*/

 

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【SQL Server 2005后推薦使用這種方式】

SQL Server 2005后之后，引入了row_number()函數，row_number()函數的分組排序功能使這種操作變得非常簡單

 

分組取TOP數據是T-SQL中的常用查詢， 如學生信息管理系統中取出每個學科前3名的學生。這種查詢在SQL Server 2005之前，寫起來很繁瑣，需要用到臨時表關聯查詢才能取到。SQL Server 2005后之后，引入了row_number()函數，row_number()函數的分組排序功能使這種操作變得非常簡單。下面是一個簡單示例： 

代碼如下:

--1.創建測試表
create table #score
(
name varchar(20),
subject varchar(20),
score int
)
--2.插入測試數據
insert into #score(name,subject,score) values('張三','語文',98)
insert into #score(name,subject,score) values('張三','數學',80)
insert into #score(name,subject,score) values('張三','英語',90)
insert into #score(name,subject,score) values('李四','語文',88)
insert into #score(name,subject,score) values('李四','數學',86)
insert into #score(name,subject,score) values('李四','英語',88)
insert into #score(name,subject,score) values('李明','語文',60)
insert into #score(name,subject,score) values('李明','數學',86)
insert into #score(name,subject,score) values('李明','英語',88)
insert into #score(name,subject,score) values('林風','語文',74)
insert into #score(name,subject,score) values('林風','數學',99)
insert into #score(name,subject,score) values('林風','英語',59)
insert into #score(name,subject,score) values('嚴明','英語',96)
--3.取每個學科的前3名數據
select * from
(
select subject,name,score,ROW_NUMBER() over(PARTITION by subject order by score desc) as num from #score
) T where T.num <= 3 order by subject
--4.刪除臨時表
truncate table #score
drop table #score

 

語法形式：ROW_NUMBER() OVER(PARTITION BY COL1 ORDER BY COL2) 
解釋：根據COL1分組，在分組內部根據 COL2排序，而此函數計算的值就表示每組內部排序后的順序編號（組內連續的唯一的)

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oracle 分組取最大值方式

 select distinct id, to_char(First_value(STARTTIME) OVER (PARTITION BY id order by to_number(VALUE) desc),'yyyy-mm-dd hh24:mi:ss') as STARTTIME,  
  First_value(ENNAME) OVER (PARTITION BY id order by to_number(VALUE) desc) as ENNAME, 
 First_value(VALUE) OVER (PARTITION BY id order by to_number(VALUE) desc) as maxvalue 
 from tab_obj_rtatt_data_old where   
  Upper(ltrim(rtrim(ENNAME))) =? 
 AND STARTTIME>=to_date(?,'YYYY-MM-DD HH24:MI:SS') 
  AND STARTTIME<=to_date(?,'YYYY-MM-DD HH24:MI:SS')