What is the function of hints in SQL?

In SQL, a hint is a directive used to instruct the database query optimizer on how to execute a query. By using hints, users can influence the execution plan of the query optimizer, thus altering the way queries are executed to improve performance or avoid potential performance issues. Hints are typically used to optimize complex queries or handle large datasets, and can instruct the database engine to use or disable specific query optimization techniques such as using indexes, merge joins, reordering, etc. However, it is important to note that using hints may cause the query to be executed differently from expected, so careful testing and evaluation are necessary when using hints.