Beginning SQL

immediately after the GROUP BY statement. For example, the following SQL creates a list of cities that
have three or more members in them:
SELECT City
FROM MemberDetails
GROUP BY City
HAVING COUNT(MemberId) >= 3;
The HAVING clause applies on a per-group basis, filtering out those groups that don’t match the condition,
whereas the WHERE clause applies on a per-record basis, filtering out records. The results for the
preceding SQL are shown in the following table:
City
Orange Town
If you take away the HAVING clause and add details of the COUNT(MemberId), your SQL is as follows:
SELECT City, COUNT(MemberId)
FROM MemberDetails
GROUP BY City;
You can see how the database gets its results:
City COUNT(MemberId)
NULL 1
Big City 2
Dover 1
New Town 1
Orange Town 4
Townsville 2
Windy Village 2
Grouping and Aggregating Data
You can see from the list that only Big City and New Town have three or more members. It’s important
to note that the WHERE clause restricts the record set that the GROUP BY clause works with. However, the
HAVING clause affects only the displayed final results. Now that you’re acquainted with the HAVING
clause’s functions, the following Try It Out shows you how to use it in SQL statements.
Try It Out Working with the HAVING Clause
1. In an earlier example, the film club’s chairperson wanted to know how many members listed
each film category as their favorite. The chairperson also wanted the list ordered from the most
popular to the least popular category. However, now the chairperson wants the list to include
only those categories where four or more members listed that category as their favorite. Execute
the following SQL to answer the chairperson’s question:
203