Question

Is is efficient to combine two queries into one? What are advantages or disadvantages?
Can someone help me combine these two queries:

SELECT quiz_id from questions WHERE question = 10

SELECT quiz_number FROM quizzes WHERE quiz_id = 5

quiz_id has 1 to many relationship with question. So for one specific question there will be only one quiz_id, but one quiz_id can have up to 20 question under it.

Answer 1

Not really sure what you mean by combine, perhaps you mean subselect / subquery? In that case try:

---    IN syntax
SELECT quiz_number FROM quizzes WHERE quiz_id IN
       (SELECT quiz_id FROM questions WHERE question = 10);

---    = syntax. This will work only if the subquery returns one value 
SELECT quiz_number FROM quizzes WHERE quiz_id = 
       (SELECT quiz_id FROM questions WHERE question = 10);