sqlserver中exec/sp_executesql的使用

--動態語句語法
/******************************************************************************************************************************************************
動態語句語法:exec/sp_executesql語法
******************************************************************************************************************************************************/
動態語句語法:
--方法1查詢表改爲動態
select * from sysobjects
exec('select ID,Name from sysobjects')
exec sp_executesql N'select ID,Name from sysobjects'--多了一個N爲unicode
--方法2:字段名，表名，數據庫名之類作爲變量時,用動態SQL 
declare @FName varchar(20)
set @FName='ID'
exec('select '+@FName+' from sysobjects where '+@FName+'=5' )
declare @s varchar(1000)
set @s=N'select '+@FName+' from sysobjects where '+@FName+'=5'
exec sp_executesql @s--會報錯
declare @s nvarchar(1000)--改爲nvarchar
set @s=N'select '+@FName+' from sysobjects where '+@FName+'=5'
exec sp_executesql @s--成功
--方法3:輸入參數
declare @i int,@s nvarchar(1000)
set @i=5
exec('select ID,Name from sysobjects where ID='+@i)
set @s='select ID,Name from sysobjects where ID=@i'
exec sp_executesql @s,N'@i int',@i--此處輸入參數要加上N
--方法4:輸出參數
declare @i int,@s nvarchar(1000)
set @s='select @i=count(1) from sysobjects'
--用exec
exec('declare @i int '+@s+' select @i')--把整個語句用字符串加起來執行
--用sp_executesql
exec sp_executesql @s,N'@i int output',@i output--此處輸出參數要加上N
select @i
--方法5:輸入輸出
--用sp_executesql
declare @i int,@con int,@s nvarchar(1000)
set @i=5
select @s='select @con=count(1) from sysobjects where ID>@i'
exec sp_executesql @s,N'@con int output,@i int',@con output ,@i 
select @con
--用exec
declare @i int,@s nvarchar(1000)
set @i=5
select @s='declare @con int select @con=count(1) from sysobjects where ID>'+rtrim(@i)+' select @con'
exec(@s)