I have 2 tables with duplicate record including 'Id' field, and I need union them.  

But I think [union all] is much more efficient than [union]  

for the reason that it need not sorting.

Following is my sql:  

SELECT \*  

FROM [dbo].[RealTime]  

**UNION ALL**  

SELECT \*  

FROM [dbo].[Query] a  

WHERE *NOT* EXISTS(  

    SELECT TOP 1 1  

    FROM [dbo].[RealTime] b  

    WHERE **a.Id = b.Id**  

 )  

 Will you have any suggestion or more elegant statement ?