When one or more relationships or connections between disparate pieces of data are needed, the PROC SQL join construct is used (see section 7.3.1).

You use a join to relate one table with another through a process known as column matching (see section 7.3.2).

You can assign table aliases to tables to minimize the number of keystrokes when referencing a table in a join query (see section 7.5.4).

When a query is placed inside the predicate of another query, it is called a subquery. Put another way, a subquery is a SELECT statement that is embedded in the WHERE clause of another SELECT statement (see section 7.7).

The IN predicate permits PROC SQL to pass multiple values from the subquery to the main query without producing an error (see section 7.7.3).

A subquery can also be constructed to evaluate multiple times, once for each row of data accessed by the main (outer) query (see section 7.7.4).

The INTERSECT operator creates an output table consisting of all the unique rows from the intersection of two query expressions (see section 7.8.1).

The UNION operator creates an output table consisting of all the unique rows from the combination of query expressions (see section 7.8.2).