从每个GROUP BY（unique_id）和ORDER BY号

Question

我有id，unique_id和order_number的表。

1. 我想通过unique_id
来分组行
2. 我想从每个组中获取MAX id行
3. 最后我想通过order_number
对行进行排序

我也有很少的WHERE条款。这是我的尝试不起作用：

SELECT MAX(id) AS id
     , order_number
  FROM table 
 WHERE final = 0 
   AND username = '$username' 
   AND active = 1 
 GROUP 
    BY unique_id 
 ORDER 
     BY order_number

Answer 1

您可以将查询用作子查询：

if(username==null || password==null){

          response.sendRedirect("Fail.jsp");
          return;
}
if (username!=null && username.equals(user)&& password.equals(pass))
        {
            response.sendRedirect("Welcome.jsp");
          return;

        }
        else {
          response.sendRedirect("Fail.jsp");
          return;
        }

或者，如果SELECT * FROM table WHERE id IN (SELECT MAX(id) AS id FROM table WHERE final=0 AND username='$username' AND active=1 GROUP BY unique_id) ORDER BY order_number 不唯一，请使用id：

JOIN

Answer 2

试试这个：

SELECT id, redni_broj 
FROM table 
WHERE final=0 AND username='$username' AND active=1 AND
    id IN (
              SELECT MAX(id) FROM table table2
              WHERE table.unique_id = table2.unique_id
          )
GROUP BY unique_id 
ORDER BY order_number;