SQL JOIN where to place the WHERE condition?

Question

I have two following examples.

1. Example (WHERE)

SELECT 1
  FROM table1 t1
  JOIN table2 t2 ON t1.id = t2.id
 WHERE t2.field = true         


        

Answer 1

JOIN conditions should normally be independent from filter conditions. You define rules of your join (the how) with ON. You filter what you want with WHERE. Performance wise, there's no general rule across all engines and designs, so your mileage will vary greatly.