How is the usage of hints in Oracle?

In Oracle database, Hints can be used to influence the query optimizer’s execution plan for better performance. Hints are a special form of comment that can provide guidance to the optimizer on how to execute the query. Common Hints include:

  1. /*+ INDEX(table_name index_name) */: Instructs the optimizer to use the specified index to execute the query.
  2. /*+ FULL(table_name) */: Instructs the optimizer to use a full table scan to execute the query.
  3. /*+ ORDERED */: Indicates the optimizer to perform join operations in the specified order as indicated in the hint.
  4. This directive instructs the optimizer to use a hash join algorithm for performing the join operation.
  5. /*+ PARALLEL(table_name, degree) */: instructs the optimizer to execute the query in parallel.

It is important to note that while hints provide suggestions for query execution plans, the database optimizer may not always follow them exactly. The actual execution plan can be influenced by other factors as well. Hints should be used cautiously, only when necessary, to avoid unnecessarily interfering with the optimizer’s decisions.

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