# JOIN operation

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

  Specifies a join between two tables with an explicit join clause. See INNER JOIN.

- LEFT OUTER JOIN

  Specifies a join between two tables with an explicit join clause, preserving unmatched rows from the first table. See LEFT OUTER JOIN.

- RIGHT OUTER JOIN

  Specifies a join between two tables with an explicit join clause, preserving unmatched rows from the second table. See RIGHT OUTER JOIN.

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.

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