MAX（）函数未按预期工作

Question

I've created sqlfiddle to try and get my head around this http://sqlfiddle.com/#!2/21e72/1

In the query, I have put a max() on the compiled_date column but the recommendation column is still coming through incorrect - I'm assuming that a select statement will need to be inserted on line 3 somehow?

I've tried the examples provided by the commenters below but I think I just need to understand this from a basic query to begin with.

Answer 1

As others have pointed out, the issue is that some of the select columns are neither aggregated nor used in the group by clause. Most DBMSs won't allow this at all, but MySQL is a little relaxed on some of the standards...

So, you need to first find the max(compiled_date) for each case, then find the recommendation that goes with it.

select r.case_number, r.compiled_date, r.recommendation
from reporting r
  join (
    SELECT case_number, max(compiled_date) as lastDate
    from reporting
    group by case_number
  ) s on r.case_number=s.case_number
      and r.compiled_date=s.lastDate

Answer 2

Thank you for providing sqlFiddle. But only reporting data is given. we highly appreciate if you give us sample data of whole tables.

Anyway, Could you try this?

SELECT
    `case`.number,
    staff.staff_name AS ``case` owner`,
    client.client_name,
    `case`.address,
    x.mx_date,
    report.recommendation
FROM
    `case` INNER JOIN (
        SELECT case_number, MAX(compiled_date) as mx_date
        FROM report
        GROUP BY case_number
    ) x ON x.case_number = `case`.number
    INNER JOIN report ON x.case_number = report.case_number AND report.compiled_date = x.mx_date
    INNER JOIN client ON `case`.client_number = client.client_number
    INNER JOIN staff ON `case`.staff_number = staff.staff_number
WHERE
    `case`.active = 1
    AND staff.staff_name = 'bob'
ORDER BY
    `case`.number ASC;

Answer 3

Check below query:

SELECT c.number, s.staff_name AS `case owner`, cl.client_name, 
       c.address, MAX(r.compiled_date), r.recommendation
FROM case c
INNER JOIN (SELECT r.case_number, r.compiled_date, r.recommendation 
            FROM report r ORDER BY r.case_number, r.compiled_date DESC
           ) r ON r.case_number = c.number
INNER JOIN client cl ON c.client_number = cl.client_number
INNER JOIN staff s ON c.staff_number = s.staff_number
WHERE c.active = 1 AND s.staff_name = 'bob'
GROUP BY c.number
ORDER BY c.number ASC

Answer 4

SELECT
case.number,
staff.staff_name AS `case owner`,
client.client_name,
case.address,
(select MAX(compiled_date)from report where case_number=case.number),
report.recommendation
FROM
case
INNER JOIN report ON report.case_number = case.number
INNER JOIN client ON case.client_number = client.client_number
INNER JOIN staff ON case.staff_number = staff.staff_number
WHERE
case.active = 1 AND
staff.staff_name = 'bob'
GROUP BY
case.number
ORDER BY
case.number ASC

try this