Beginning SQL

Chapter 8
260
Now you need to find a list of cities in which a meeting has never been held:
SELECT LocationId, City
FROM Location
WHERE LocationId NOT IN (SELECT LocationId FROM Attendance);
The subquery is used to find all LocationIds from the Location table that are not in the Attendance table.
This subquery provides the following results:
LocationId City
3 Big City
Now you need to combine the WHERE clauses and add them to a DELETE statement. Doing so combines
the WHERE clause of the preceding query, which included the following condition:
LocationId NOT IN (SELECT LocationId FROM Attendance);
Likewise, it combines the SELECT statement of the first example as a subquery:
SELECT COUNT(*), City
FROM MemberDetails
GROUP BY City, State;
The condition and the subquery are merged into the WHERE clause of the DELETE statement:
DELETE FROM Location
WHERE (SELECT COUNT(*) FROM MemberDetails
WHERE Location.City = MemberDetails.City
AND
Location.State = MemberDetails.State
GROUP BY City, State)