1.1 About Sub Queries
- A Sub query or Inner query or a Nested query is a query within another SQL query and embedded within the WHERE clause.
- Sub queries can be used with the SELECT, INSERT, UPDATE, and DELETE statements along with the operators like =, <, >, >=, <=, IN, BETWEEN, etc.
- Sub queries must be enclosed within parentheses.
- A sub query can have only one column in the SELECT clause, unless multiple columns are in the main query for the sub query to compare its selected columns.
- An ORDER BY command cannot be used in a sub query, although the main query can use an ORDER BY. The GROUP BY command can be used to perform the same function as the ORDER BY in a sub query.
- Sub queries that return more than one row can only be used with multiple value operators such as the IN operator.
- A sub query cannot be immediately enclosed in a set function.
- The BETWEEN operator cannot be used with a sub query. However, the BETWEEN operator can be used within the sub query.
Last modified: Tuesday, 7 January 2020, 10:21 AM