MySQL groupwise MAX() returns unexpected results

Question

TABLE: LOAN

Loan_no     Amount        SSS_no              Loan_date

7           700.00        0104849222          2010-01-03 
8                    


        

Answer 1

The MySQL reference suggests several ways to solve this. The simplest is a subquery:

SELECT *
FROM   loan l1
WHERE  loan_date=(SELECT MAX(l2.loan_date)
              FROM loan l2
              WHERE l1.sss_no = l2.sss_no);

Given that this type of subqueries potentially have bad performance, they also suggest using a JOIN (essentially Mahmoud Gamal's answer):

SELECT l1.loan_no, l1.amount, l1.sss_no, l1.loan_date
FROM loan l1
JOIN (
  SELECT loan_no, MAX(loan_date) AS loan_date
  FROM loan
  GROUP BY sss_no) AS l2
  ON l1.loan_date = l2.loan_date AND l1.sss_no = l2.sss_no;

A third option is:

SELECT l1.loan_no, l1.amount, l1.sss_no, l1.loan_date
FROM loan l1
LEFT JOIN loan l2 ON l1.sss_no = l2.sss_no AND l1.loan_date < l2.loan_date
WHERE l2.sss_no IS NULL;

The LEFT JOIN works on the basis that when l1.loan_date is at its maximum value, there is later l2.loan_date, so the l2 row values will be NULL.

All these should have the same output, but likely differ in performance.