Update script is changing the number of records for the values updated each time I run the query

[Tetol]

I have a a query result set in a temp table1 with 5 columns.
AcctNum, Location, GroupName, Count1, Count2. Columns Count1 and Count tow has 1s and nulls in it all the way through. I intend to sum these columns and group by Location, GroupName in a later step.

I need to update the GroupName column in table1 from another temp table2 where I have Distinct records of 3 columns. AcctNum, Location, GroupName2.

My update script is:

Update table1
Set GroupName = table2.GroupName2
From table1 Left Outer Join
table2 on table1.AcctNum = table2.AcctNum AND table1.Location = table2.Location

However, the number of occurrences of 1s in column1 and column2 keep changing for those records that were updated by the update script each time I run the script to validate the numbers. I am not sure what this keeps happening. Any Thoughts? see attached for sample tables and expected result without change to column1 and column2 values.

Thank you

 

[carp]

Try this:

Update table1
Set GroupName = (SELECT table2.GroupName2
                   From table2 
                  WHERE table1.AcctNum = table2.AcctNum 
                    AND table1.Location = table2.Location);