无法从嵌套选择的列 sql 中选择顶行

Question

我有两张桌子

产品

PID  NAME                ORIGINAL_PRICE    DISCNT_RATE
---- -----------         --------------    -----------
p001 stapler                      9.99          .1
p002 TV                           249           .15
p003 camera                       148           .2

购买

  PUR# EID PID  CID         QTY PTIME     TOTAL_PRICE
------ --- ---- ---- ---------- --------- -----------
100001 e01 p002 c001          1 12-AUG-17      211.65
100002 e01 p003 c001          1 20-SEP-17       118.4
100003 e02 p004 c002          5 08-OCT-17        4.95
100005 e04 p007 c004          1 15-OCT-17       119.2
100006 e03 p008 c001          1 12-OCT-17       349.3

根据总数量查找销量最多的每种产品的 pid 和名称。显示相应的总数量（标题：“总销售量”）。使用列格式将标题更改为“销售总量”。

溶胶：

到目前为止我所做的是

 SELECT Max("Total") AS "HS", pid 
 from (Select pid, sum(qty) as "Total"
 from purchases group by pid);

如果可以提供任何帮助，我将无法按预期处理信息..

P.S: 这不是作业

Answer 1

您可以使用 Sum 和 group by 来获取总值，并在排序结果上使用 TOP 1 来获取最大值

在 SQL 服务器中

  select TOP 1 a.PID, sum(b.QTY) as "total quantity sold"
  FROM Products AS a
  INNER JOIN Purchases AS b on a.PID  = b.PID
  GROUP BY a.pID
  ORDER BY sum(b.QTY) DESC 

像您所做的那样使用子选择中的最大值（不使用 group by 仅获取一行）.. 可能会产生错误的结果，因为在大多数数据库中这是不允许的，或者可以显示为子选择的结果集..

如果您不想使用 TOP（行限制），则应在子选择的适当位置使用过滤器的最大值并获得正确的耦合 PID、MAX tital

Answer 2

对于销量最大的产品的pid和名称：

从 Oracle 12c 开始，fetch 功能将输出限制为一行：

SELECT pu.pid, pr.name, sum(pu.qty) as "total quantity sold"
FROM PURCHASES pu
INNER JOIN PRODUCTS pr on pu.pid = pr.pid
GROUP BY pu.pid, pr.name
ORDER BY sum(pu.qty) DESC
FETCH FIRST 1 ROWS ONLY
;

对于支持 row_number() over() 的早期版本的 Oracle（或对于具有相同功能支持的其他数据库）：

SELECT pid, name, "total quantity sold"
FROM (
      SELECT pu.pid, pr.name, sum(pu.qty) as "total quantity sold"
           , ROW_NUMBER() OVER(ORDER BY sum(pu.qty) DESC) AS RN
      FROM PURCHASES pu
      INNER JOIN PRODUCTS pr on pu.pid = pr.pid
      GROUP BY pu.pid, pr.name
      ) 
WHERE RN = 1
;

但这两种方法都假设只有一行要报告。在一组更大的数据中，可能有不止一行共享最高数量的总和。要返回所有此类行，请改用dense_rank() over()，例如：

SELECT pid, name, "total quantity sold"
FROM (
      SELECT pu.pid, pr.name, sum(pu.qty) as "total quantity sold"
           , DENSE_RANK() OVER(ORDER BY sum(pu.qty) DESC) AS RNK
      FROM PURCHASES pu
      INNER JOIN PRODUCTS pr on pu.pid = pr.pid
      GROUP BY pu.pid, pr.name
      ) 
WHERE RNK = 1
;

请注意，在提供的示例中，产品表中缺少 PID p004/p007/p008。我认为这只是问题中的一个遗漏。

SQL Fiddle

Oracle 11g R2 架构设置：

CREATE TABLE PURCHASES
    (PURno int, EID varchar2(3), PID varchar2(4), CID varchar2(4), QTY int, PTIME timestamp, TOTAL_PRICE numeric)
;

INSERT ALL 
    INTO PURCHASES (PURno, EID, PID, CID, QTY, PTIME, TOTAL_PRICE)
         VALUES (100001, 'e01', 'p002', 'c001', 1, '12-Aug-2017 12:00:00 AM', 211.65)
    INTO PURCHASES (PURno, EID, PID, CID, QTY, PTIME, TOTAL_PRICE)
         VALUES (100002, 'e01', 'p003', 'c001', 1, '20-Sep-2017 12:00:00 AM', 118.4)
    INTO PURCHASES (PURno, EID, PID, CID, QTY, PTIME, TOTAL_PRICE)
         VALUES (100003, 'e02', 'p004', 'c002', 5, '08-Oct-2017 12:00:00 AM', 4.95)
    INTO PURCHASES (PURno, EID, PID, CID, QTY, PTIME, TOTAL_PRICE)
         VALUES (100005, 'e04', 'p007', 'c004', 1, '15-Oct-2017 12:00:00 AM', 119.2)
    INTO PURCHASES (PURno, EID, PID, CID, QTY, PTIME, TOTAL_PRICE)
         VALUES (100006, 'e03', 'p008', 'c001', 1, '12-Oct-2017 12:00:00 AM', 349.3)
SELECT * FROM dual
;
CREATE TABLE PRODUCTS
    (PID varchar2(5), NAME varchar2(70), ORIGINAL_PRICE int, DISCNT_RATE numeric)
;

INSERT ALL 
    INTO PRODUCTS (PID, NAME, ORIGINAL_PRICE, DISCNT_RATE)
         VALUES ('p001', 'stapler', 9.99, .1)
    INTO PRODUCTS (PID, NAME, ORIGINAL_PRICE, DISCNT_RATE)
         VALUES ('p002', 'TV', 249, .15)
    INTO PRODUCTS (PID, NAME, ORIGINAL_PRICE, DISCNT_RATE)
         VALUES ('p003', 'camera', 148, .2)
    INTO PRODUCTS (PID, NAME, ORIGINAL_PRICE, DISCNT_RATE)
         VALUES ('p004', 'p004 missing from sample', 0, 0)
    INTO PRODUCTS (PID, NAME, ORIGINAL_PRICE, DISCNT_RATE)
         VALUES ('p007', 'p007 missing from sample', 0, 0)
    INTO PRODUCTS (PID, NAME, ORIGINAL_PRICE, DISCNT_RATE)
         VALUES ('p008', 'p008 missing from sample', 0, 0)
SELECT * FROM dual
;

查询 1：

SELECT PID, NAME, "total quantity sold"
FROM (
      SELECT pu.pid, pr.name, sum(pu.qty) as "total quantity sold"
           , ROW_NUMBER() OVER(ORDER BY sum(pu.qty) DESC) AS RN
      FROM PURCHASES pu
      INNER JOIN PRODUCTS pr on pu.pid = pr.pid
      GROUP BY pu.pid, pr.name
      ) 
WHERE RN = 1
;

Results：

|  PID |                     NAME | total quantity sold |
|------|--------------------------|---------------------|
| p004 | p004 missing from sample |                   5 |

查询 2：

SELECT PID, NAME, "total quantity sold"
FROM (
      SELECT pu.pid, pr.name, sum(pu.qty) as "total quantity sold"
           , DENSE_RANK() OVER(ORDER BY sum(pu.qty) DESC) AS RNK
      FROM PURCHASES pu
      INNER JOIN PRODUCTS pr on pu.pid = pr.pid
      GROUP BY pu.pid, pr.name
      ) 
WHERE RNK = 1
;

Results：

|  PID |                     NAME | total quantity sold |
|------|--------------------------|---------------------|
| p004 | p004 missing from sample |                   5 |