Question

Trying to get a simple COUNT from a table that takes a couple of joins and some math. I can’t get it right. I keep running into “invalid use of group function.” In a similar query I get get all the data, just can’t get a count.

I have 4 tables.

CUSTOMERS
id  name  thegroup periodicity
1   Foo     3        4

GROUPS
id  group_name
3    New York

Each customer has a series of pickup dates.

COLLECTIONS
id  coll_date   customer_id
3   2011-09-07  1
3   2011-07-21  1

And a periods table which is the number of weeks between scheduled pickups.

PERIODS
id  duration
4   4

So a duration of 4 means pickup every 4 weeks, or 28 days.

I can calculate when the next pickup date is getting close: If they have a periodicity of 28 days, then when it has been 21 days since the last pickup it is time to flag it. In that case it would be 75% through its periodicity 21/28, or:

(ABS(DATEDIFF(MAX(collections.coll_date), NOW())) / (periods.duration *7))

If that result is greater than .75, then they are due for a pick up.
I can loop through customers and calculate that no problem.

My goal is:
I need to know how many customers in each group are due for pick up, re: COUNT(customers) WHERE (this calculation) > .75 GROUP BY group.id.

I have this so far, but can’t get it right.

SELECT COUNT(*), groups.id
FROM customers
INNER JOIN groups ON customers.thegroup = groups.id
INNER JOIN periods ON customers.periodicity = periods.id
LEFT JOIN collections ON customers.id = collections.rest_id
WHERE  status = 1 AND (ABS(DATEDIFF(MAX(collections.coll_date), NOW()))/(periods.duration*7)) > .75
GROUP BY groups.id

Answer 1

To list all groups with at least one customer having at least one pickup due according to your calculation and it shows how many customers have a pickup due use the following

SELECT 
C.THEGROUP,
COUNT(DISTINCT C.ID) CNT
FROM CUSTOMERS C 
INNER JOIN PERIODS P ON C.PERIODICITY = P.ID
LEFT OUTER JOIN (SELECT CL.REST_ID CUSTID, MAX (CL.COLL_DATE) MCOLLD FROM COLLECTIONS CL GROUP BY CL.REST_ID) X ON C.ID = X.CUSTID
WHERE C.STATUS = 1 AND (ABS(DATEDIFF(X.MCOLLD, NOW()))/(P.DURATION*7)) > .75
GROUP BY C.THEGROUP

IF you want all groups listed including those not having any pickups use

SELECT G.ID, IFNULL (A.CNT, 0) CNT FROM
GROUPS G
LEFT OUTER JOIN
(
SELECT 
C.THEGROUP,
COUNT(DISTINCT C.ID) CNT
FROM CUSTOMERS C 
INNER JOIN PERIODS P ON C.PERIODICITY = P.ID
LEFT OUTER JOIN (SELECT CL.REST_ID CUSTID, MAX (CL.COLL_DATE) MCOLLD FROM COLLECTIONS CL GROUP BY CL.REST_ID) X ON C.ID = X.CUSTID
WHERE C.STATUS = 1 AND (ABS(DATEDIFF(X.MCOLLD, NOW()))/(P.DURATION*7)) > .75
GROUP BY C.THEGROUP
) A ON G.ID = A.THEGROUP
ORDER BY G.ID