Question

I need to know, how do i do this on the fly,

for example i have customers who are in the each different duedate statuses, i want to select MAX (most recent due date) ON LEFT JOIN currently when its join two tables it selects the oldest duedate which is not what i want..

SELECT c.customerid, i.datedue
                        FROM  customers c
                               LEFT JOIN invoice i 
                                 ON i.customerid = c.customerid
                        WHERE  i.datedue <= UNIX_TIMESTAMP()
                               AND c.status!='d'
                        GROUP  BY i.customerid
                        ORDER BY i.datedue DESC
                        LIMIT  0, 1000

Answer 1

You need to use the max() function:

SELECT c.customerid, MAX(i.datedue)
FROM customers c LEFT JOIN invoice i ON i.customerid = c.customerid
WHERE i.datedue <= UNIX_TIMESTAMP() and c.status!='d'
GROUP BY i.customerid
ORDER BY i.datedue DESC
LIMIT 0,1000

This will give you the maximum datedue for each customer.