The Optimizer can only optimize data access for those SQL statements that contain a search condition. A search condition is defined with a WHERE clause.
SELECT name
FROM customer
WHERE city = 'Seattle' AND zip > 98101
You can combine the following SQL key words with a search condition: SELECT, UPDATE, DELETE, INSERT.
Some search condition restrictions apply to UPDATE statements.
The form of the search condition has a significant effect on the costs incurred by executing the SQL statement. When determining costs for an SQL statement, the Optimizer only considers the following search conditions:
If the search conditions in an SQL statement cannot be transformed into one of the forms listed above, the Optimizer cannot determine a search strategy for them and uses the sequential search instead.
If search conditions are linked using a number of identical Boolean operators, the sequence of these conditions does not affect how the Optimizer determines the search strategy.