Beginning SQL

City State
Orange Town New State
Windy Village Golden State
Big City Mega State
It may be easier to think of the ON clause as a WHERE clause that joins tables. The preceding SQL uses an
AND operator to join the two conditions, but you can use any of the logical operators.
Cross Joins
A cross join is the most basic join, as there’s no ON clause to join the tables. Instead, all the rows from all
the tables listed in the join are included in the results set. Only the usual filtering clauses associated with
SELECT statements, such as a WHERE clause, limit the results set. You can define a cross join in two ways.
The first way of creating a cross join uses the CROSS JOIN statement, as shown in the following code,
where the Category and Location tables are cross-joined:
SELECT Category, Street
FROM Category CROSS JOIN Location
ORDER BY Street;
The preceding syntax is supported by Oracle, MySQL, and SQL Server, but not by IBM’s DB2 or MS
Access. An alternative syntax for a cross join is simply to list all the tables to be cross-joined in the FROM
clause, as shown here:
SELECT Category, Street
FROM Category, Location
ORDER BY Street;
Virtually all databases support the second way of cross joining, so it’s likely the best way to perform a
cross join. Both of the preceding queries do the same thing and produce the same results, which are
shown here:
Category Street
Thriller Main Street
Romance Main Street
Horror Main Street
War Main Street
Sci-fi Main Street
Historical Main Street
Comedy Main Street
Thriller Tiny Terrace
Selecting Data from Different Tables
Table continued on following page
213