Without a WHERE clause, is supposed to return all the data in the table, and so a table scan is the correct (if not desirable) behavior. (For more information, see .)

creates indexes on tables in the following situations:

• When you define a primary key, unique, or foreign key constraint on a table. See "CONSTRAINT clause" in the for more information.
• When you explicitly create an index on a table with a CREATE INDEX statement.

For an index to be useful for a particular statement, one of the columns in the statement's WHERE clause must be the first column in the index's key.

For a complete discussion of how indexes work and when they are useful, see and .

Indexes provide some other benefits as well:

• If all the data requested are in the index, does not have to go to the table at all. (See .)
• For operations that require a sort (ORDER BY), if uses the index to retrieve the data, it does not have to perform a separate sorting step for some of these operations in some situations. (See .)

See "CREATE INDEX statement" in the for details on creating indexes, including restrictions on key size.