Combining Columns And Grouping By....

Hi,
I have the following SQL

SELECT Table1.Col1, Table3.Col1 AS Expr1,
COUNT(Table1.Col2) AS Col2_No, COUNT(Table1.Col3) AS Col3_No etc,
FROM Table3
INNER JOIN Table2 ON Table3.Col1=Table2.Col1
RIGHT OUTER JOIN Table1 ON Table2.Col2=Table2.Col2
GROUP BY Table1.Col1, Table3.Col1

The output rows have a value in either Table1.Col1 or Table3.Col1 but not
both.
I'd like to combine Table1.Col1 and Table3.Col1 and group by the combined
column in the result but don't know how.
Thanks gratefully