Using subqueries saves you steps. For example, if you want to find all books that are the same price as Straight Talk About Computers, you can perform the task in two steps (or use a subquery). First, find the price of Straight Talk:
SELECT price
FROM titles
WHERE title = 'Straight Talk About Computers'
price
---------
19.99
(1 row(s) affected)
Now use the result (the price) in a second query to find all books that cost the same as Straight Talk:
SELECT title, price FROM titles WHERE price = $19.99
title |
price |
--------------------------------------------- |
------- |
The Busy Executive's Database Guide |
19.99 |
Straight Talk About Computers |
19.99 |
Silicon Valley Gastronomic Treats |
19.99 |
Prolonged Data Deprivation: Four Case Studies |
19.99 |
(4 row(s) affected) |
By using a subquery, you can solve the problem with a single statement:
SELECT title, price
FROM titles
WHERE price =
(SELECT price
FROM titles
WHERE title = 'Straight Talk About Computers')