What are the different scenarios in which the ‘limit’ clause is used in Oracle?

In Oracle database, the LIMIT statement is not directly supported, but you can achieve similar functionality using ROWNUM and subqueries. Here are some scenarios where this can be useful:

1. Pagination query: By limiting the number of rows returned using ROWNUM, pagination functionality can be achieved.
2. Top-N query: Limit the result set to the top N rows by using the ROWNUM and ORDER BY clauses, achieving a Top-N query.
3. Random sampling: You can use the ROWNUM and ORDER BY clauses to randomly order the result set, and then restrict the number of rows returned to achieve random sampling functionality.
4. Grouping query: Using ROWNUM and subqueries can achieve limitation of grouping result sets, for example, only returning the first N rows in each group.
5. To retrieve data from the past N months or days, you can use the ROWNUM and ORDER BY clauses to sort and limit the number of rows returned, allowing you to obtain data from the desired time frame.

It is worth noting that in Oracle databases, ROWNUM is calculated after the query result is returned, so when using functionality similar to LIMIT, it is necessary to combine it with subqueries. Additionally, Oracle databases also provide the syntax FETCH FIRST N ROWS ONLY to achieve similar functionality to LIMIT.