What is sub query in MS Access?

Answer 1

It is a query inside another query. Normally it is a select statement inside a query. Sometimes you want to run query and use data from another query in that query. So you will have one query inside another one. The inside or nested query is the subquery.

Answer 2

It is a form inside another form. It is often used where tables are related, particularly in one to many relationships. So you could have a main form which shows the details of a class in a college and a subform which shows details of the people who are taking that class. When you view a different class, the list of students will automatically change too. The class would be from one table and the students from another, with the two tables being related to each other. The two forms can be created separately and then one put into the other. The sub form can also be viewed on its own.