Question

How can you refer to the “combined entity” created from an outer join within your query? Specifically how can you replace the “??” in the query below:

SELECT TableA.x, 
       ??.y --How do you select from the combined entity?
  FROM TableA, 
       TableB buys 
FULL OUTER JOIN TableB sells ON buys.run_id = sells.run_id 
                            AND buys.specie_id = sells.specie_id 
                            AND buys.account_id = sells.account_id
WHERE TableA.id = ?? 
  AND -- want to join this with the "combined entity" resulting from the outer join
      buys.buy = 'Y' 
  AND -- Is this valid or does this have to be within the Outer join statement?
      sells.buy = 'N';

Answer 1

Presumably what you’re trying to ask is how to refer to the columns used in the join in other parts of the query. There is no joined entity per se; you still have to refer to the columns from the tables (in this case “buys” or “sells”, it just happens that the columns used in the join will have the same value for both tables.

If you want whichever is not null (since this is a full outer join), you can use coalesce or nvl to find find the non-null value:

SELECT TableA.x, 
       nvl(buys.run_id,sells.run_id) as run_id,
       ...