What should be considered when using the rownum function in SQL?

When using the ROWNUM function in SQL, it is important to keep the following points in mind:

1. ROWNUM is a pseudo column unique to Oracle databases that is used to identify the sequence number of rows returned in a result set, which is assigned only after the result set is returned.
2. ROWNUM is assigned after the query result is returned, so it cannot be directly used for filtering conditions in the WHERE clause.
3. To use ROWNUM for filtering conditions in query results, wrap ROWNUM in a subquery and then use it in the outer query.
4. Be cautious when using ROWNUM in the ORDER BY clause, as ROWNUM is assigned after the query results are returned, making it unreliable to use ROWNUM before sorting.
5. When using ROWNUM, make sure the query results are ordered to avoid unexpected outcomes because ROWNUM is assigned after the query results are returned.
6. In Oracle 12c and later versions, the replacement function for ROWNUM is ROW_NUMBER() OVER(), which offers more flexibility and better performance.