Question

I’m not very good at using complicated MySQL, so I’m stuck with a somewhat complicated (but still pretty basic, I think) situation:

I have 3 tables:

• Table A has 2 records, one with ID 1, one with ID 2. They both have a
  foreign key to Table B, which is the same.
• Table B currently has only
  one record, but will have more in the future.
• Table C has multiple
  records, all with a reference to either record 1 or 2 in Table A.

What I want to achieve:
I want to select all (or some) information about Table A’s records, but only for those records that reference to the record in Table B. Now here’s the catch for me: I want to order the results, starting with the one which has the most records in Table C referring to it.

So:

    SELECT COUNT(C.*) AS NUMBER_OF_RECORDS, A.* 
    FROM `TableA` A, `TableB` B, `TableC` C
    WHERE A.bID = 1 AND C.aID = A.ID
    ORDER BY NUMBER_OF_RECORDS DESC;

Something like that, except that this doesn’t work for C.aID = A.ID. I hope the above query will just make my intentions more clear.

Any help greatly appreciated!

Better view of the situation with sample data

Tables:

1. Department
2. Location
3. Employee

So now say, I would want to select all data of the departments in one location, ordered by the amount of employees.

Desired output:

---

departmentID, departmentName, no_of_emps
1, Sales, 14
2, Finance, 12
3, Management, 6

Answer 1

SELECT 
       COUNT(C.aID) AS NUMBER_OF_RECORDS
     , A.* 
  FROM 
       `TableA` A
    JOIN 
       `TableB` B
      ON B.ID  = A.bID 
    LEFT JOIN                       --- so you also get rows from A (and B)
       `TableC` C                   --- that have no matching rows in C
      ON C.aID = A.ID
GROUP BY
    A.ID
ORDER BY 
    NUMBER_OF_RECORDS DESC;