Question

I’m working on a query wherein I have three tables to join, however the third table may or may not have a relevant record.

I currently have:

  SELECT table1.val, table2.val, table.3.val 
  FROM
      table1
      LEFT JOIN table2
          ON table1.val = table2.val
      LEFT JOIN table3 
          ON table.3.val = table2.val
  WHERE
      table1.name = "name" 
      AND table3.name = 'certain name'
  ORDER BY table1.val ASC

How can I write this so that if 'certain name' doesn’t exist in table3, that portion is omitted from the WHERE and SELECT clauses? I’m actually selecting several more fields but this should adequately demonstrate the problem.

Answer 1

If you mean that result form table3 should only be visible, if the table3.val is equal to the table2.val AND that the table3.name should equal 'certain name', then this will fit you:

SELECT table1.val, table2.val, table.3.val 
FROM table1
LEFT JOIN table2
ON table1.val = table2.val
LEFT JOIN table3 
ON table.3.val = table2.val AND table3.name = 'certain name'
WHERE table1.name = "name" 
ORDER BY table1.val ASC

After all, this is what LEFT JOIN is for…