What are the hints in Oracle?
An Oracle hint provides directive to the optimizer in choosing an execution plan for the SQL statement being executed. The Oracle INDEX hint instructs the optimizer to use an index scan for the specified table. Use the INDEX hint for function-based, domain, B-tree, bitmap, and bitmap join indexes.
How do I create an index in Oracle?
Introduction to Oracle CREATE INDEX statement To create a new index for a table, you use the CREATE INDEX statement as follows: CREATE INDEX index_name ON table_name(column1[,column2,…]) Second, specify the name of the table followed by one or more indexed columns surrounded by parentheses.
What is materialize hint in Oracle?
The Oracle materialize hint is used to ensure that the Oracle cost-based optimizer materializes the temporary tables that are created inside the “WITH” clause. This is not necessary in Oracle10g, but it helps ensure that the tables are only created one time.
What is an Oracle index?
An index is a schema object that contains an entry for each value that appears in the indexed column(s) of the table or cluster and provides direct, fast access to rows. Oracle Database supports several types of index: Normal indexes. (By default, Oracle Database creates B-tree indexes.)
How to force Oracle to use an index?
The easiest way to force index usage is with the index hint. When forcing an index, always use the table alias whenever you have a query that specifies an alias. For example, the following query will force the use of the dept_idx index because the emp table is aliased with “e”: select /*+ index (e,dept_idx) */ * from emp e;
Why is Oracle not using my index?
Oracle not using an index can be due to: · Bad/incomplete statistics – Make sure to re-analyze the table and index with dbms_stats to ensure that the optimizer has good metadata. · Wrong optimizer_mode – The first_rows optimizer mode is to minimize response time, and it is more likely to use an index than the default all_rows mode.
How does Oracle use index?
Context indexes – You can use Oracle text indexes to remove full-table scans when using the LIKE operator.
Why is query not using index in Oracle?
Other indexes: You may have other indexes that Oracle perceives as being “better” for the query. In sum, the Oracle optimizer should immediately see a new index and begin using it immediately, invalidating all SQL that might benefit from the index. When Oracle does not use an index, you can force him to use the index with diagnostic tools.