Querying data from multiple tables using subqueries is a great capability, but it doesn’t always give you everything you need, and the syntax can become a bit messy and confusing. Also, as discussed in the previous chapter, when a sub-query executes for each match of an outer query, performance can be affected. For this reason, SQL allows you to query multiple tables simultaneously with a simpler syntax. This capability doesn’t completely replace some of the techniques you saw in the previous chapter involving subqueries across multiple tables, but it’s extremely powerful when you simply want a result set that contains information from more than one table. Because relational databases are designed to hold data in more than one table, where records in one table are usually associated with records in other tables, this functionality is essential.
KeywordsPrevious Chapter Source Table Class Table Multiple Table Simple Syntax
Unable to display preview. Download preview PDF.