declare @date varchar(10)
    declare @month int
    declare @year int
    set  @month=datepart(mm,getdate())
    set  @year=datepart(yy,getdate())

    
    exec('select distinct convert(varchar(10),logindate,120) 
    from dbo.BoxLogMonth'+@year+@month+'
    where datediff(dd,logindate,getdate())=1')

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