1:
普通sql语句可以用exec执行
eg: select * from tablename
exec('select * from tablename')
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 = '[name]'
select @fname from sysobjects -- 错误
exec('select ' + @fname + ' from sysobjects') -- 请注意 加号前后的 单引号的边上要加空格
exec sp_executesql n' select ' + @fname + ' from sysobjects'
当然将字符串改成变量的形式也可
declare @s varchar(1000)
set @s = 'select ' + @fname + ' from sysobjects'
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 sysobjects'
exec(@s) -- 成功
exec sp_executesql @s -- 此句正确，
3: 输出参数
eg:
declare @num,
@sqls
set @sqls='select count(*) from ' + @servername + '.a.dbo.b'
exec(@sqls)
我如何能将exec执行的结果存入变量@num中
declare @num int,
@sqls nvarchar(4000)
set @sqls='select @a=count(*) from '+@servername+'.a.dbo.b'
exec sp_executesql @sqls,n'@a int output',@num output
select @num
