SQL & PL/SQL

I am working on some complicated subqueries in Oracle 10g. I read all the documentation, I have reference books and files, and...google. I was hoping, someone might be able to provide a thorough explanation in their own words.

This is my understanding of the matter.

SELECT column1, column2
FROM table1, table2
WHERE join conditions
AND search field1 =
(SELECT column3, column4
FROM table3, table4
WHERE search and join condition0

Now, regarding AND search field1 =, must it be the same as column3 in the sub? How do I know which condition should be set aside for = (Subquery)?


thank you