What is a sub query? What are its various types?

- Sub Query also termed as Nested Query or Inner Query is used to get data from multiple tables.
- A sub query is added in the where clause of the main query.

There can be two types of subqueries:

a.) Correlated sub query
- It can reference column in a table listed in the from list of the outer query but is not as independent as a query. .

b.) Non-Correlated sub query
- Results of this sub query are submitted to the main query or parent query.
- It is independent like a query

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