sqlserver中exec/sp_executesql的使用

--动态语句语法
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动态语句语法:exec/sp_executesql语法
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动态语句语法:
--方法1查询表改为动态
select * from sysobjects
exec('select ID,Name from sysobjects')
exec sp_executesql N'select ID,Name from sysobjects'--多了一个N为unicode
--方法2:字段名，表名，数据库名之类作为变量时,用动态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--会报错
declare @s nvarchar(1000)--改为nvarchar
set @s=N'select '+@FName+' from sysobjects where '+@FName+'=5'
exec sp_executesql @s--成功
--方法3:输入参数
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--此处输入参数要加上N
--方法4:输出参数
declare @i int,@s nvarchar(1000)
set @s='select @i=count(1) from sysobjects'
--用exec
exec('declare @i int '+@s+' select @i')--把整个语句用字符串加起来执行
--用sp_executesql
exec sp_executesql @s,N'@i int output',@i output--此处输出参数要加上N
select @i
--方法5:输入输出
--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)