Let's say you have divided the query output into multiple groups with the GROUP BY clause. Now you are only interested in some of the groups, not all the groups. If you want to filter out some groups from the query, you can apply filtering criteria at the group level by using the HAVING clause inside the GROUP BY clause with this syntax:

SELECT group_level_fields FROM source_tables

WHERE search_condition

GROUP BY group_by_expression

HAVING group_filtering_condition

Since group_filtering_condition applies to groups, only group level expressions can be used in group_filtering_condition. The following tutorial exercise gives you some good examples of HAVING clause:

SELECT tag, COUNT(*), MIN(created), AVG(counts)

FROM ggl_links

GROUP BY tag HAVING AVG(counts) > 300

GO

tag COUNT(*) MIN(created) AVG(counts)

DBA 3 2005-01-01 774

SQA 2 2003-01-01 778

SELECT tag, COUNT(*), MIN(created), AVG(counts)

FROM ggl_links

GROUP BY tag

HAVING AVG(counts) > 300 AND tag = 'DBA'

GO

tag COUNT(*) MIN(created) AVG(counts)

DBA 3 2005-01-01 774

Note that the more criteria you have in the HAVING clause, the less groups you will get.