What is sub query and its properties?
A sub-query is a query which can be nested inside a main query like Select, Update, Insert or Delete statements. This can be used when expression is allowed. Properties of sub query can be defined as
A sub query should not have order by clause
A sub query should be placed in the right hand side of the comparison operator of the main query
A sub query should be enclosed in parenthesis because it needs to be executed first before the main query
More than one sub query can be included
