In the previous chapters, the queries could be classified as being relatively simple because references were always made against a single table. We now turn our attention to queries of a more complex nature that call on the full features of the SQL procedure. Four complex query constructs will be illustrated in this chapter.
Inner Joins
Up to 32 tables are referenced in a FROM and optional WHERE clause of a SELECT statement.
Outer Joins
A maximum of two tables are referenced in a FROM and ON clause of a SELECT statement.
Subqueries
A query is embedded (nested) in the WHERE clause of a main query.
Set Operations
A new results table is created from two separate queries.