如何计算 SQL 中 select 的结果

Question

I was given the following question for an assignment

Write a SQL statement to show the sum of Hours Worked for each Type of OWNER but exclude services of employees who have Experience Level of Junior and exclude any Owner Type with Less Than Four members

I'm having a hard time figuring out how to accomplish the last part of the question. I believe that it would require counting a portion of a select statement but I'm not sure how to do that.

So far, this is what I have:

 SELECT SUM(HoursWorked), OwnerType 
 FROM PROPERTY_SERVICE 
 JOIN EMPLOYEE ON EMPLOYEE.EmployeeID=PROPERTY_SERVICE.EmployeeID
 JOIN OWNED_PROPERTY ON OWNED_PROPERTY.PropertyID = PROPERTY_SERVICE.PropertyID
 INNER JOIN OWNER ON OWNER.OwnerID=OWNED_PROPERTY.OwnerID 
 WHERE NOT EMPLOYEE.ExperienceLevel='Junior' 
 *This is where I believe the solution should go*
 GROUP BY OWNER.OwnerType;

Answer 1

Presumably, you just want a HAVING clause:

SELECT SUM(HoursWorked), o.OwnerType 
FROM PROPERTY_SERVICE ps
JOIN EMPLOYEE e        ON e.EmployeeID  = ps.EmployeeID
JOIN OWNED_PROPERTY op ON op.PropertyID = ps.PropertyID
INNER JOIN OWNER o     ON o.OwnerID     = op.OwnerID 
WHERE e.ExperienceLevel <> 'Junior' 
GROUP BY o.OwnerType
HAVING COUNT(*) < 4

This excludes groups of rows having the same OwnerType that contain less than 4 rows. You might need to adjust the expression to your exact definition of a member .

Note that I added table aliases to the query to make it easier to read and write. I would also recommend prefixing column HoursWorked with the table it belongs to, to avoid ambiguity.