Associating tables in SQL is usually a breeze. But what happens when you find yourself looking at the completely wrong set of records and you don't know why? Find out how correctly applying joins can help you understand and avoid these mysterious data returns.
by Susan Sales Harkins,
Patricia E. O' Connor
September 23, 2003
he cornerstone of the relational database system is its multiple tables and the ability to associate those tables with one another so you can combine data from different but related tables. Most of the time these associations are intuitive and work just as you expect. However, problems can arise when one of these associations returns unexpected results. In other words, the records you get, aren't the records you know you should be seeing.
Fortunately, you can dynamically relate different tables by applying what's known as a join. Technically, a join is the operation used when selecting data to create these relationships at retrieval time. What that means to you is that a join determines which records are selected and which aren't. In this article, we'll introduce you to several types of joins supported by SQL and show you how to correctly apply them to get the data you need.
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he cornerstone of the relational database system is its multiple tables and the ability to associate those tables with one another so you can combine data from different but related tables. Most of the time these associations are intuitive and work just as you expect. However, problems can arise when one of these associations returns unexpected results. In other words, the records you get, aren't the records you know you should be seeing.
