MAX（）函数如预期

Question

我创建sqlfiddle，试图让我的头围绕这个http://sqlfiddle.com/#!2/21e72/1

在查询不工作，我穿上了compiled_date列max()，但建议仍列通过未来不正确 - 我假设select语句需要插入第3行？

我试过下面的评论者提供的例子，但我想我只是需要从一个基本的查询来理解这一点开始。

Answer 1

正如其他人所指出的那样，问题是，一些列的SELECT既不聚集也不group by子句中使用。大多数数据库管理系统根本不会允许这样做，但MySQL在某些标准上稍微放松了一些......

因此，您需要先为每种情况找到max(compiled_date)，然后查找与之相关的建议。

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

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 

试试这个

Answer 3

检查下面的查询：

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

感谢你们提供了sqlFiddle。但只提供报告数据。我们非常感谢您给我们提供整个表格的样本数据。

无论如何，你可以试试这个吗？

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;