Question

I have 3 tables t1, t2, t3. I want a result set based on these conditions : t1 with outer join on t2 (all rows of t1), t1 with outer join on t3 (all rows of t1) and t2 with outer join on t3 (all rows of t2). How to use these outer 3 joins in a single query?
Basically I want to convert a t-sql format query to ANSI format. The original query is something like this

Select * from t1, t2, t3
where t1.col1 *= t2.col1
  and t1.col2 *= t3.col1
  and t2.col2 *= t3.col2

I managed to use first 2 joins as

   Select * 
     from t1
left join t2 on t1.col1 = t2.col1
left join t3 on t1.col2 = t3.col1

This works properly for first 2 conditions. But wasn’t able to incorporate the 3rd join. Can anyone please suggest a way to accompolish this?
Thanks in advance.

Answer 1

From your question I guess you only want rows from t3 that join with the rows from t2 that joined with t1:

SELECT 
    * 
FROM
    t1
    LEFT JOIN t2 ON t1.col1 = t2.col1
    LEFT JOIN t3 ON t1.col2 = t3.col1 AND t2.col2 = t3.col2

This will not include rows from t2 and t3 that join on col2, unless the rows from t2 have already joined with t1 on col1.