# HAVING clause

A HAVING clause restricts the results of a GROUP BY in a selectExpression.

The HAVING clause is applied to each group of the grouped table, much as a WHERE clause is applied to a select list. If there is no GROUP BY clause, the HAVING clause is applied to the entire result as a single group. The SELECT clause cannot refer directly to any column that does not have a GROUP BY clause. It can, however, refer to constants, aggregates, and special registers.

See selectExpression for more information.

## Syntax

    HAVING booleanExpression

The booleanExpression can contain only grouping columns (see GROUP BY clause), columns that are part of aggregate expressions, and columns that are part of a subquery. For example, the following query is illegal, because the column SALARY is not a grouping column, it does not appear within an aggregate, and it is not within a subquery:

    -- SELECT COUNT(*)
    -- FROM SAMP.STAFF
    -- GROUP BY ID
    -- HAVING SALARY > 15000

Aggregates in the HAVING clause do not need to appear in the SELECT list. If the HAVING clause contains a subquery, the subquery can refer to the outer query block if and only if it refers to a grouping column.

## Example

    -- Find the total number of economy seats taken on a flight,
    -- grouped by airline,
    -- only when the group has at least 2 records.
    SELECT SUM(ECONOMY_SEATS_TAKEN), AIRLINE_FULL
    FROM FLIGHTAVAILABILITY, AIRLINES
    WHERE SUBSTR(FLIGHTAVAILABILITY.FLIGHT_ID, 1, 2) = AIRLINE
    GROUP BY AIRLINE_FULL
    HAVING COUNT(*) > 1

Parent topic: SQL clauses