What are the Properties and Different Types of Sub-Queries?

Properties of a Sub-Query

• A sub-query must be enclosed in the parenthesis.
• A sub-query must be put on the right hand of the comparison operator, and
• A sub-query cannot contain an ORDER BY clause, however sub-query can use ORDER BY when used with TOP clause.

Types of Sub-query

• Single-row sub-query, where the sub-query returns only one row.
• Multiple-row sub-query, where the sub-query returns multiple rows, and
• Multiple column sub-query, where the sub-query returns multiple columns