Does the order of tables in a join matter, when LEFT (outer) joins are used?

Question

I would like to confirm that the SQL query

SELECT ....
  FROM apples,
       oranges
       LEFT JOIN kiwis ON kiwis.orange_id = oranges.id,
       bananas
          


        

Answer 1

The situation is summarized at Controlling the Planner with Explicit JOIN Clauses. Outer joins don't get reordered, inner ones can be. And you can force a particular optimizer order by dropping *join_collapse_limit* before running the query, and just putting things in the order you want them it. That's how you "hint" at the database in this area.

In general, you want to use EXPLAIN to confirm what order you're getting, and that can sometimes be used to visually confirm that two queries are getting the same plan.