Procedurally transform subquery into join

Question

Is there a generalized procedure or algorithm for transforming a SQL subquery into a join, or vice versa? That is, is there a set of typographic operations that can be appli

Answer 1

At a really high level. to transform a sub-query to a JOIN:

1. FROM: Table Names go into FROM
   • JOIN The parts of the WHERE clause with table names on both sides determine (a) the type of JOIN (b) the condition of join
   • WHERE The parts of the where clause without table names on both sides go into the WHERE clause
   • SELECT Column names from Sub-Query go into the SELECT

Transforming a JOIN to Sub-Query entails the reverse of the above logic