select the max value and other values from three different tables - mysql

Question

I have three tables with the following structure:-
CREATE TABLE `contract` (
`conid` int(11) NOT NULL AUTO_INCREMENT,
`servName` int(11) NOT NULL,
`cid` int(11) NOT NULL,
`term` int(11) DEFAULT NULL,
`monthly_charge` double NOT NULL,
`start_date` date NOT NULL,
`expiry_Date` date NOT NULL,
`next_PayDate` date DEFAULT NULL,
`status` tinyint(4) NOT NULL,
PRIMARY KEY (`conid`),
UNIQUE KEY `servName` (`servName`,`cid`)
)
CREATE TABLE `servicetype` (
`sid` int(11) NOT NULL AUTO_INCREMENT,
`serviceName` varchar(255) NOT NULL,
PRIMARY KEY (`sid`)
)
CREATE TABLE `transactions` (
`tid` int(11) NOT NULL AUTO_INCREMENT,
`conid` int(11) NOT NULL,
`amount` double NOT NULL,
`paidate` date NOT NULL,
`descr` text NOT NULL,
PRIMARY KEY (`tid`)
)
What I want to get is the latest transaction for a particular user i.e:-
conid, serviceName, cid, term, monthly_charge, start_date, expiry_Date, next_PayDate, amount, paidate, descr
And this is the select statement I am using the get to that information:-
SELECT c.conid, serviceName, cid, term, monthly_charge, start_date, expiry_Date, next_PayDate, status, amount, paidate, descr
FROM servicetype s
LEFT JOIN contract c on s.sid = c.servName
LEFT JOIN transactions t ON c.conid=t.conid
WHERE cid = 4 AND status = 1
The statement works but, it is giving me all transactions belonging to cid 4 and all I want to display is only the latest transaction belonging to the said contract it (conid).
Thanking you in advance for your time and effort.

Answer 1

Sounds like you want to use MySQL's GROUP BY to group all of the results by a specific cid, and then use a HAVING condition to get the MAX() transaction:
SELECT
c.conid, serviceName, cid, term, monthly_charge, start_date, expiry_Date, next_PayDate, status, amount, paidate, descr
FROM servicetype s
LEFT JOIN contract c on s.sid = c.servName
LEFT JOIN transactions t ON c.conid=t.conid
WHERE
cid = 4 AND status = 1
GROUP BY cid
HAVING t.paidate = MAX(t.paidate)

Answer 2

You can JOIN twice on the transactions table. The first join gets the max() date for each conid and then the second join will return the details of that max transaction:
select c.conid,
s.serviceName,
c.cid,
c.term,
c.monthly_charge,
c.start_date,
c.expiry_date,
c.next_PayDate,
c.status,
t2.amount,
t1.paidate,
t2.descr
FROM servicetype s
LEFT JOIN contract c
on s.sid = c.servName
LEFT JOIN
(
SELECT max(paidate) paidate, conid
FROM transactions
GROUP BY conid
) t1
ON c.conid=t1.conid
LEFT JOIN transactions t2
ON t1.paidate = t2.paidate
AND t1.conid = t2.conid
WHERE c.cid = 4
AND c.status = 1
Edit, based on your comments the query should be:
select c.conid,
s.serviceName,
c.cid,
c.term,
c.monthly_charge,
c.start_date,
c.expiry_date,
c.next_PayDate,
c.status,
t3.amount,
t3.paidate,
t3.descr
FROM servicetype s
LEFT JOIN contract c
on s.sid = c.servName
LEFT JOIN
(
SELECT max(paidate) paidate, conid, max(tid) tid
FROM transactions t
GROUP BY conid
) t1
on c.conid = t1.conid
LEFT JOIN transactions t3
on t1.conid = t3.conid
and t1.paidate = t3.paidate
and t1.tid = t3.tid
where c.cid = 4
and c.status = 1
GROUP BY c.conid;
See SQL Fiddle With Demo