MSSQL - Union Query

[Mark Gambo]

I am designing a Union query between to tables in order to sum to like fields:

SELECT OBJNUM, Sum(SUM1) AS HASH
FROM (
     SELECT Table1.OBJNum AS OBJNUM, Sum(Table1.EMPNUM) as Sum1
     FROM Table1
     GROUP BY Table1.OBJNum
     
     UNION

     SELECT Table2.OBJNum AS OBJNUM,  Sum(Table2.VENNUM) as Sum1
     FROM Table2
     GROUP BY Table2.OBJNum
     )
GROUP BY OBJNUM;

I was wondering if it would be more efficent if if I just sum'ed the Sum1 Fields in the Main Query like This:

SELECT OBJNUM, Sum(SUM1) AS HASH
FROM (
     SELECT Table1.OBJNum AS CASENUM, Table1.EMPNUM as Sum1
     FROM Table1
     GROUP BY Table1.OBJNum, Table1.EMPNUM

     UNION

     SELECT Table2.OBJNum AS OBJNUM,  Table2.VENNUM as Sum1
     FROM Table2
     GROUP BY Table2.OBJNum, Table2.VENNUM
     )
GROUP BY OBJNUM;

Any thoughts?