The JOIN operations, which are among the possible TableExpressions in a FROM clause,
perform joins between two tables. (You can also perform a join between two
tables using an explicit equality test in a WHERE clause, such as "WHERE t1.col1
= t2.col2".)
Syntax
JOIN Operation
The
JOIN operations are:
- INNER JOIN operation
Specifies a
join between two tables with an explicit join clause.
- LEFT OUTER JOIN operation
Specifies a
join between two tables with an explicit join clause, preserving unmatched
rows from the first table.
- RIGHT OUTER JOIN operation
Specifies a
join between two tables with an explicit join clause, preserving unmatched
rows from the second table.
- CROSS JOIN operation
Specifies a
join that produces the Cartesian product of two tables. It has no explicit join
clause.
- NATURAL JOIN operation
Specifies an inner or outer join between two tables. It has no
explicit join clause. Instead, one is created implicitly using the
common columns from the two tables.
In all cases, you can specify additional restrictions on one
or both of the tables being joined in outer join clauses or in the WHERE
clause.
JOIN expressions and query optimization
For information
on which types of joins are optimized, see Tuning Derby.
