1、行列转换

问题：假设有张学生成绩表(tb)如下:

【资料图】

想变成(得到如下结果)：

代码：

WITH tb(姓名,课程,分数) AS(SELECT N"张三",N"语文",74UNION ALLSELECT N"张三",N"数学",83UNION ALLSELECT N"张三",N"物理",93UNION ALLSELECT N"李四",N"语文",79UNION ALLSELECT N"李四",N"数学",86UNION ALLSELECT N"李四",N"物理",88)SELECT 姓名 ,MAX(CASE 课程 WHEN "语文" THEN 分数 ELSE 0 END) 语文,MAX(CASE 课程 WHEN "数学" THEN 分数 ELSE 0 END) 数学,MAX(CASE 课程 WHEN "物理" THEN 分数 ELSE 0 END) 物理FROM tb GROUP BY  姓名

2、分页

方案一：利用NOT IN和SELECT TOP分页语句形式

SELECT TOP 10 * FROM TestTableWHERE ID NOT IN(SELECT TOP 20 ID FROM TestTable ORDER BY ID)ORDER BY ID

方案二：利用ID大于多少和SELECT TOP分页语句形式

SELECT TOP 10 * FROM TestTableWHERE ID > (SELECT MAX(id) FROM (SELECT TOP 20 id FROM TestTable ORDER BY id) AS T)ORDER BY ID

方案三：利用SQL Server中的特性ROW_NUMBER进行分页

SELECT * FROM (  SELECT ROW_NUMBER() OVER(ORDER BY ID DESC) AS ROWID,*  FROM TestTable) AS mytable where ROWID between 21 and 40

3、结果合并

合并重复行

SELECT * FROM AUNIONSELECT * FROM B

不合并重复行

SELECT * FROM AUNION ALLSELECT * FROM B

4、随机排序

SELECT * FROM TestTable ORDER BY NEWID()

还可以结合TOP取随机的前N条记录

SELECT TOP 100 * FROM TestTable ORDER BY NEWID()

5、以任意符号分隔取两边数据

例如我们以逗号(,)来分割数据，将如下数据

分割成如下图所示：

SELECT R,CASE WHEN  CHARINDEX(",",R)>1 THEN  LEFT(R,CHARINDEX(",",R)-1) ELSE NULL END AS R1 ,CASE WHEN CHARINDEX(",",R)>1 THEN RIGHT(R,(LEN(R) - CHARINDEX(",",R))) ELSE NULL END AS R2FROM  t

代码较长，我们对代码进行拆分来理解：

SELECT  CHARINDEX(",",",") --结果是1SELECT  CHARINDEX(",","NULL") --结果是0SELECT  CHARINDEX(",","") --结果是0SELECT  CHARINDEX(",","A,B") --结果是2SELECT  LEN("A,B") --结果是3SELECT  LEN("A,B") - CHARINDEX(",","A,B") --结果是3-2=1SELECT  RIGHT("A,B",( LEN("A,B") - CHARINDEX(",","A,B"))) --结果是 B

最后一步我们将"A,B"拆分出来了B，同理A我们也可以用类似的方法获取到。

6、WAITFOR延时执行

例 等待1小时2分零3秒后才执行SELECT语句

WAITFOR DELAY "01:02:03"SELECT * FROM Employee

其中 DELAY是在延时多长时间后才开始执行。

例等到晚上11点零8分后才执行SELECT语句

WAITFOR TIME "23:08:00"SELECT * FROM Employee

其中TIME是等到具体某个时刻才开始执行​

关键词： 开始执行 如下图所示 多长时间