动态sql语句基本语法

1 :普通SQL语句可以用Exec执行

eg: Select * from tableName

Exec('select * from tableName')

Exec sp_executesql N'select * from tableName' -- 请注意字符串前一定要加N

2:字段名，表名，数据库名之类作为变量时，必须用动态SQL

eg:

declare @fname varchar(20)

set @fname = 'FiledName'

Select @fname from tableName -- 错误,不会提示错误，但结果为固定值FiledName,并非所要。

Exec('select ' + @fname + ' from tableName') -- 请注意 加号前后的 单引号的边上加空格

当然将字符串改成变量的形式也可

declare @fname varchar(20)

set @fname = 'FiledName' --设置字段名

declare @s varchar(1000)

set @s = 'select ' + @fname + ' from tableName'

Exec(@s) -- 成功

exec sp_executesql @s -- 此句会报错

declare @s Nvarchar(1000) -- 注意此处改为nvarchar(1000)

set @s = 'select ' + @fname + ' from tableName'

Exec(@s) -- 成功

exec sp_executesql @s -- 此句正确

3. 输出参数

declare @num int,

@sqls nvarchar(4000)

set @sqls='select count(*) from tableName'

exec(@sqls)

--如何将exec执行结果放入变量中？

declare @num int,

@sqls nvarchar(4000)

set @sqls='select @a=count(*) from tableName '

exec sp_executesql @sqls,N'@a int output',@num output

select @num

例:

set ANSI_NULLS ON

set QUOTED_IDENTIFIER ON

go

-- =============================================

-- Create date: 2008.03.22

-- Description: 验证用户存在性

-- =============================================

ALTER PROCEDURE [dbo].[Proc_CheckUser]

@CheckName varchar (50) ,

@Result varchar(20) OUtPUT

AS

BEGIN

SET NOCOUNT ON;

declare @WhereStr varchar (500), @SQLStr Nvarchar(4000),@re bit

IF(left(@CheckName,5)='95002' and isnumeric(@CheckName)=1) SET @CheckName=substring(@CheckName,6,len(@CheckName))-- 登陆号码前+95002

IF(isnumeric(@CheckName)=1) SET @WhereStr='UID = '''+@CheckName+''''-- 登陆号码前+95002

IF((left(@CheckName,2)='13' OR left(@CheckName,2)='15' and len(@CheckName)=11) and isnumeric(@CheckName)=1) SET @WhereStr='Phone = '''+@CheckName+''''-- 手机号码

IF(left(@CheckName,1)='0' and isnumeric(@CheckName)=1 and (len(@CheckName) between 10 and 13)) SET @WhereStr='TelePhone = '''+@CheckName+'''' -- 固定电话

IF(Charindex('@',@CheckName)>0 and Charindex('.',@CheckName)>0 and isnumeric(@CheckName)=0) SET @WhereStr='Email = '''+@CheckName+'''' -- email

SET @SQLStr = 'set @re=case when exists(select 0 from Passport_Account where '+@WhereStr+' and 1=1) then 1 else 0 end'

exec sp_executesql @SQLStr,N'@re bit output,@WhereStr varchar(500)',@re output,@WhereStr

if @re=1

BEGIN

SET @SQLStr=N'select @Result=UID from Passport_Account where '+@WhereStr+' and 1=1'

exec sp_executesql @SQLStr ,N'@Result varchar(20) output,@WhereStr varchar(500)',@Result output,@WhereStr

SET @Result='1'+@Result

Print @Result

END

ELSE

BEGIN

SET @Result=0

print 0

END

END