Question

I have two tables which I am left joining together.

SELECT Col3, tab1.Col1, tab1.Col2 FROM
    (SELECT Col1,Col2 
    FROM Table1
    GROUP BY Col1,Col2) tab1
LEFT JOIN
    (SELECT Col3, Col1, Col2
    FROM Table2
    GROUP BY Col3, Col1, Col2) tab2
ON tab2.Col2 = tab1.Col2 AND tab2.Col1 = tab1.Col1

At the moment for the rows in Table1 which do not exist in Table2 I return a row where Col3 is Null. As I am grouping data based on Col3, it would be good if I could somehow get the value of Col3 instead of Null…..

Is this possible??

So I am trying to return every possible combination of col1 and col2, per value of col3. The problem is when col3 does not contain a particular combination of col1,col2 I am getting nulls for col3…

Answer 1

Assuming Col3 is some kind of category, and is a primary key of a category table, you might do this:

select Category.Col3,
       tab1.Col1,
       tab1.Col2,
       sum (tab2.YourAggregate) SumOfSomething
 -- Take all categories
  from Category
 -- Cartesian product with Tabl1
 cross join Table1 tab1
 -- Find matching records in Table2, if they exist
  left join Table2 tab2
    on Category.Col3 = Tab2.Col3
   and Tab1.Col1 = Tab2.Col1
   and Tab1.Col2 = Tab2.Col2
 group by Category.Col3,
       tab1.Col1,
       tab1.Col2

Cross join produces Cartesian product of tables involved, retrieving Col3 which might not be found in Table2.