Let’s say we want to display names and marks of all students who have scored marks greater than the marks scored by the student Cisco.

To solve this problem, we first need to figure out the marks scored by Cisco, using the query below:

We get the answer as 65, and then we can use it to get the names and marks of all students who scored more marks:

We get the right answer. But the same problem can be solved by firing a single query, using a concept called SUBQUERY. Have a look at the query below:

Notice, the result of the query inside the parentheses is supposed to be equivalent to either some marks (an integer), or a NULL value, both of which can be put in a filter query for marks. So, the query itself can be used as part of the filter. Such a query is called a subquery.