如何從MySQL中選擇總和（最大剩余（x + y + z））以捕獲總和（1200 + 1300 + 1400）

Question

如何sum(max remain(x + y + z)) from MySQL中選擇sum(max remain(x + y + z)) from ，以捕獲sum(1200+1300+1400) ？

id | user | remain
-----------------
1  | x   | 1000
----------------
2  | x   | 1200
----------------
3  | y   | 1100
----------------
4  | y   | 1300
----------------
5  | z   | 1200
----------------
5  | z   | 1400
----------------
using (SqlConnection cn = new SqlConnection(Class1.x))
        {
            cn.Open();
            string cm1 = "select sum(max remain(all users)) as 'total' from item_new_company";
            using (SqlCommand cmd = new SqlCommand(cm1, cn))
            {
                using (SqlDataReader dr = cmd.ExecuteReader())
                { dr.Read(); tot5 = dr["total"].ToString(); }
            }
        }

Answer 1

像這樣：

SELECT SUM(MaxRemain) TotalOfMaxRemains
FROM
(
    SELECT MAX(remain) AS MaxRemain
    FROM item_new_company
    GROUP BY user
) AS t;

SQL小提琴演示

結果：

| TOTALOFMAXREMAINS |
---------------------
|              3900 |

---

子查詢：

SELECT MAX(remain) AS MaxRemain
FROM item_new_company
GROUP BY user

使用GROUP BY user和MAX(remain) ，將為您提供每個user的remain最大值，然后在外部查詢中， SUM將為您提供總數。

---

更新資料

對於SQL Server，以前的查詢應該可以正常工作，但是還有另一種方法：

WITH CTE AS
(
  SELECT *, ROW_NUMBER() OVER(PARTITION BY [user] 
                              ORDER BY id DESC) AS rownum 
  FROM item_new_company 
) 
SELECT SUM(remain) AS Total 
FROM CTE 
WHERE rownum = 1;

SQL小提琴演示