SQL基础系列(3)-变量、函数、存储过程等

1.    变量

 定义变量

 DECLARE @a INT

 赋值

 SET @a=1

 PRINT @a

 DECLARE @name NVARCHAR(30)

 --select 赋值

 SELECT @name='zcx'

 PRINT @name

 SELECT @name=FirstName FROM dbo.Persons

 PRINT @name

 DECLARE @name NVARCHAR(50)

 --update 赋值

 UPDATE  Persons

 SET     @name = FirstName

 WHERE   ID = 1

 PRINT @name

2.    临时表

--创建临时表1

 create table #persion

 (

      [id] [int]  NOT NULL,

      [name] [nvarchar](5) NOT NULL,

      [pwd] [nvarchar](20) NULL

 )

 insert into #persion values(1,'zcx','')

 SELECT * INTO #psersion1 FROM #persion

 select * from #persion UNION ALL select * from #psersion1

 DROP TABLE #persion

 DROP TABLE #psersion1

插入select的数据

insert into #persion select id,FirstName,LastName from dbo.Persons

注意和select into的区别

Select into 会创建新的临时表

修改临时表结构

alter table #persion add [tmpid] int NOT NULL IDENTITY(10,1)

alter table #persion add [tmpid1] uniqueidentifier NOT NULL default(newid())

给查询结果集增加自增长列

要求主表Persons没得主键

select IDENTITY(int,1,1)as ID, * into #temp from Persons

SELECT * FROM #temp

和count性质类似

select SUM(1) from Persons

有主键的表添加列

select (select SUM(1) from Persons where id<= a.id) as myID,* from Persons a order by myID

创建表变量：下面代码要同时执行

 declare @mytable table

 (

     id int not null,

     name nvarchar(50) null

 )

 INSERT INTO @mytable

         ( id, name )

 VALUES  ( 0, -- id - int

           N'zcx'  -- name - nvarchar(50)

           )

          INSERT INTO @mytable

                  ( id, name )

          VALUES  ( 0, -- id - int

                    N'zjj'  -- name - nvarchar(50)

                    )

 select * from @mytable

3.    循环

 DECLARE @index INT

 DECLARE @resukt INT

 SET @index = 1

 SET @resukt = 0

 WHILE @index <= 100

     BEGIN

         SET @resukt += @index

         SET @index += 1

     END

 PRINT @resukt

4.    条件

 IF ( 3 > 5 )

     BEGIN

         PRINT 'true'

     END

 ELSE

     BEGIN

         PRINT 'false'

     END

 When then

 DECLARE @num INT

 DECLARE @name NVARCHAR(30)

 SET @num = 3

 SET @name = CASE WHEN @num = 1 THEN 'elephant'

                  WHEN @num = 2 THEN 'hippo'

                  WHEN @num = 3 THEN 'trigger'

                  ELSE 'false'

             END

 PRINT @name

5.    游标

原则上尽量不要使用游标

(更多信息：http://www.cnblogs.com/moss_tan_jun/archive/2011/11/26/2263988.html)

DECLARE @name NVARCHAR(30)

DECLARE mycursor CURSOR FOR SELECT FirstName FROM dbo.Persons

--打开游标

 OPEN mycursor

 WHILE @@FETCH_STATUS=0

 BEGIN

     FETCH NEXT FROM mycursor INTO @name

     PRINT @name

 END

 CLOSE mycursor

 --回收

 DEALLOCATE mycursor

6.    触发器

触发器中的临时表：

Inserted

存放进行insert和update 操作后的数据

Deleted

存放进行delete 和update操作前的数据

 Create trigger persion_update

     On dbo.Persons

     for Update

 As

     declare @msg nvarchar(50)

     --@msg记录修改情况

     select @msg = N'姓名从“' + Deleted.FirstName + N'”修改为“' + Inserted.FirstName + '”' from Inserted,Deleted

     --插入日志表

     insert into TAB(Col2)values(@msg)

7.    存储过程

 DROP PROCEDURE compute_add

 CREATE PROCEDURE compute_add

     @p1 INT ,

     @p2 INT ,

     @p3 INT OUTPUT

 AS

     BEGIN

         SET @p3=@p1+@p2

     END

     DECLARE @result INT

     EXEC compute_add 1,2,@result OUTPUT

     PRINT @result

8.    函数

标量函数

 CREATE FUNCTION COMPUTE_ADD ( @p1 INT, @p2 INT )

 RETURNS INT

 AS

     BEGIN

         RETURN @p1+@p2

     END

调用方式

DECLARE @result INT

SET @result=dbo.COMPUTE_ADD(1,2)

PRINT @result

表值函数

 CREATE FUNCTION mytable ( @id INT )

 RETURNS TABLE

 AS

 RETURN

     ( SELECT    *

       FROM      dbo.Persons

       WHERE     id < @id

     )

调用方式

select * from dbo.mytable(3)

表值函数：返回指定的列

 CREATE FUNCTION mytable ( @id INT )

 RETURNS @table TABLE

     (

       firstname NVARCHAR(50) ,

       lastname NVARCHAR(50)

     )

 AS

     BEGIN

         INSERT  INTO @table

                 SELECT  firstname ,

                         lastname

                 FROM    dbo.Persons

                 WHERE   id < @id

         RETURN

 END

调用方式

select * from dbo.mytable(3)

函数和存储过程区别