Question

我有此表结构和示例数据。此表中有销售订单的迭代。最初，要求鼠标15 Qty。后来买方决定更新Qty并将其设置为25，然后再次意识到他只需要20。因此，我想从销售订单中获取特定商品的最新行。

CREATE TABLE SaleOrder
(
ID INT PRIMARY KEY,
Item VARCHAR(25),
Qty INT
)

INSERT INTO SaleOrder VALUES (1, 'Mouse', 15);
INSERT INTO SaleOrder VALUES (2, 'Key Board', 10);
INSERT INTO SaleOrder VALUES (3, 'Printer', 3);
INSERT INTO SaleOrder VALUES (4, 'Mouse', 25);
INSERT INTO SaleOrder VALUES (5, 'Mouse', 20);

这是我写的查询。

SELECT ID, Item, Qty
FROM SaleOrder M
WHERE ID = (SELECT MAX(ID) FROM SaleOrder S WHERE S.ID = M.ID GROUP BY Item)

预期的输出结果应该包含3行。

ID  Item       Qty
1   Mouse      15
2   Key Board  10
3   Printer    3
4   Mouse      25
5   Mouse      20

我这里缺少什么吗？

Answer 1

您可以尝试使用ROW_NUMBER窗口函数来使每个Item最多获得一个

SELECT ID,Item,Qty
FROM (
   SELECT *,ROW_NUMBER() OVER(PARTITION BY Item ORDER BY ID DESC) rn
   FROM SaleOrder
) t1
where rn = 1

SQLfiddle

Answer 2

您可以使用以下两种方法之一：

使用SQL> create table test (col varchar2(10)); Table created. SQL> insert into test values ('abc'); 1 row created. SQL> select length(col) from test; LENGTH(COL) ----------- 3 SQL> insert into test values (rpad('def', 10, ' ')); 1 row created. SQL> select col, length(col) len from test; COL LEN ---------- ---------- abc 3 def 10 SQL>

ROW_NUMBER()

使用子查询

;WITH CTE
AS
(
    SELECT
        RN = ROW_NUMBER() OVER(PARTITION BY Item ORDER BY Id DESC),
        *
        FROM SaleOrder
)
SELECT
    *
    FROM CTE
        WHERE RN = 1

结果

SELECT
    *
    FROM SaleOrder SO
        WHERE ID = (
            SELECT MAX(ID) FROM SaleOrder WHERE Item = SO.Item
        )-- You Don't Need the Group By Here

Answer 3

您可以使用MAX尝试以下查询。

SELECT SaleOrder.* FROM (
SELECT MAX(Id) as Id, Item FROM SaleOrder Group By Item
)a INNER JOIN SaleOrder ON a.Id = SaleOrder.Id

或者您也可以使用以下

SELECT *
FROM SaleOrder D
WHERE Id = (SELECT MAX(Id) FROM SaleOrder WHERE Item = D.Item)

两种情况下的输出如下所示

ID  Item        Qty
--------------------
3   Printer      3
5   Mouse       20
2   Key Board   10

您可以在此处查看演示-Group By Max Demo

在特定列上分组时如何获取MAX ID？

3 个答案: