Suppose you want to find the books that have the same price as Straight Talk About Computers. First, you find the price of Straight Talk:
select price from titles where title = "Straight Talk About Computers"
price ------------- $19.99 (1 row affected)
You use the results of the first query in a second query to find all the 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 rows affected)
You can use a subquery to receive the same results in only one step:
select title, price from titles where price = (select price from titles where title = "Straight Talk About Computers")
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 rows affected)
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