Beginning SQL Queries: From Novice to Professional, Second Edition

© Clare Churcher 2016

Clare Churcher, Beginning SQL Queries, 10.1007/978-1-4842-1955-3_5

5. Self Joins

Clare Churcher¹ 

(1)Studio B Productions, Great Neck, New York, USA

When we select a subset of rows based on a condition in a WHERE clause, the condition is evaluated for each row independently. An example might be a query to find all the members who have entered tournament 36. The condition TourID = 36 can be evaluated for each row in the Entry table to achieve the required result. However, if we want to find members who have entered both tournaments 36 and 24, we cannot do this by inspecting just one row of the Entry table. We need to find two rows (or entries) for the same member—one for each of the specified tournaments. A simple WHERE clause ...