What hints are used in Oracle to speed up queries?

In Oracle, various hints are used to speed up queries, which influence the query optimizer. Some commonly used hints:

• /*+ INDEX(table_name index_name) */ — forces the use of a specific index.
• /*+ FULL(table_name) */ — forces a full table scan.
• /*+ NO_MERGE(table_name) */ — prevents merging of views or subqueries.
• /*+ LEADING(table1 table2) */ — sets the join order of tables.
• /*+ USE_NL(table1 table2) */ — uses nested loops for joins.
• /*+ PARALLEL(table_name, degree) */ — enables parallel execution of the query.

Example of using a hint:

SELECT /*+ INDEX(emp emp_dept_idx) */ * FROM emp WHERE dept_id = 10;

Hints help the optimizer choose a more efficient execution plan, especially in complex queries or with non-standard data.