SQL查询 - RowNumber、循环、行列转换_row number转换-优快云博客

本文介绍了SQL中的几种实用技巧，包括使用RowNumber进行行编号、通过While循环实现批量数据插入、利用游标遍历数据集以及如何进行行列转换等操作。

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1.RowNumber用法：
Row_Number() over (order by col desc)
Row_Number() over (partiton by colA,colB order by colA) //按colA,colB分组后按colA排序

2.while嵌套循环

declare @CourseNum int
declare @ChapterNum int
set @ChapterNum=1
set @CourseNum=1
while(@courseNum<=10)
 begin
  declare @courseName varchar(30)
  set @CourseName='Course'+Convert(Varchar(30),@courseNum)
  insert into course values(@CourseName)
 while(@ChapterNum<=20)
  begin
   declare @ChapterName varchar(40)
   set @ChapterName=@courseName+'_Chapter'+Convert(Varchar(30),@ChapterNum)
   insert into chapter values(@ChapterName,@CourseNum)
   set @ChapterNum=@ChapterNum+1
   continue
  end
set @ChapterNum=1--一定要再重置它的值 否则 它一直保持为 20
set @courseNum=@courseNum+1
continue
end
select * from chapter

3.游标循环

DECLARE
   @id    INT, @value VARCHAR(10);
 BEGIN
   -- 定义游标.
   DECLARE c_test_main CURSOR FAST_FORWARD FOR
     SELECT id, value FROM test_main;
   -- 打开游标.
   OPEN c_test_main;
   --填充数据.
   FETCH NEXT FROM c_test_main INTO @id, @value;
   --假如检索到了数据，才处理.
   WHILE @@fetch_status = 0
   BEGIN
     PRINT @value;
     --填充下一条数据.
     FETCH NEXT FROM c_test_main INTO @id, @value;
   END;
   -- 关闭游标
   CLOSE c_test_main;
   --释放游标.
   DEALLOCATE c_test_main;
 END;

4.行列转换

select Student as '姓名',
max(case Subject when '语文' then Score else 0 end) as '语文' ,--如果这个行是“语文”，就选此行作为列
max(case Subject when '英语' then Score else 0 end ) as '英语'
from Scores
group by Student
order by Student

另外一种方法，用pivot

/*
pivot(
　　聚合函数(要转成列值的列名)
　　for 要转换的列
　　in（目标列名）
　　)
*/
select Student as '姓名',
avg(语文) as '语文',
avg(英语) as '英语'
from Scores
pivot(
    avg(Score) for Subject 
    in (语文,英语)
    )as NewScores
group by Student
order by Student asc

行列转换转自：http://www.cnblogs.com/oneivan/archive/2012/02/16/2353796.html