The INDEX_DESC hint explicitly chooses an index scan for the specified table. When the statement uses an index assortment scan, then Oracle scans the index entries in descending order of their indexed values. Inside a partitioned index, the outcomes are in descending order within Every single partition.
Use with the USE_NL and USE_MERGE hints is recommended with the ORDERED hint. Oracle uses these hints once the referenced table is forced to be the inner table of the be a part of; the hints are overlooked In case the referenced desk will be the outer table.
Specifying a person of such hints causes the optimizer to settle on the specified accessibility path only if the accessibility route is obtainable depending on the existence of the index or cluster and about the syntactic constructs of your SQL statement. If a hint specifies an unavailable entry route, then the optimizer ignores it.
In case the UNNEST trace is used, Oracle to start with verifies In case the assertion is legitimate. If your assertion is not really valid, then subquery unnesting simply cannot proceed. The statement need to then should go a heuristic examination.
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You may ship hints for just a SQL statement into the optimizer by enclosing them in a comment within the statement.
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The cardinality statistic is used, if it exists. When there is a predicate, dynamic sampling is done with a table trace and cardinality will not be estimated.
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The REWRITE trace forces the cost-dependent optimizer to rewrite a query regarding materialized views, when feasible, without cost consideration.
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In lots of situations, a nested loops be a part of returns the initial row quicker than a sort merge sign up for. A nested loops sign up for can return the 1st row immediately after looking at the 1st chosen row from a single table and the primary matching row from another and combining them, while a form merge be part of can not return the very first row until just after looking through and sorting all selected rows of both tables after which you can combining the primary rows of each and every sorted row source.
By way of example, you could recognize that a particular index is more selective for specified queries. According to this information, there's a chance you're capable to choose a more efficient execution plan in comparison to the optimizer. In such a scenario, use hints to force the optimizer to make use of the optimal execution prepare.