Question

我写了一个查询，我想显示＆＃34;客户编号＆＃34; （CUSTOMER表），＆＃34;发票数量＆＃34; （INVOICE表），这是每个客户的总发票，以及＆＃34; Total Cus Purchases＆＃34; （通过加入CUSTOMER，INVOICE和LINE表计算得出），这是属于每个客户的所有发票中所有购买的总和。

第一个查询吐出错误的＆＃34;发票数量＆＃34;。

--First Query    
SELECT CUSTOMER.CUST_NUM AS "Customer Number",
COUNT(INVOICE.INV_NUM) AS "Number of Invoices",
SUM(LINE.LINE_UNITS * LINE.LINE_PRICE) AS "Total Cus Purchases"
FROM CUSTOMER
JOIN INVOICE
ON CUSTOMER.CUST_NUM = INVOICE.CUST_NUM
JOIN LINE
ON INVOICE.INV_NUM = LINE.INV_NUMBER
GROUP BY CUSTOMER.CUST_NUM;

Customer Code Number of Invoices Total Cus Purchases

     1000              5              188.72
     1003              6               432.8
     1001              3               34.92
     1002              1               70.44

但是，第二个查询（省略LINE的连接语句时会注意到这一点，用于计算＆＃34; Total Cus Purchases＆＃34;）吐出正确的＆＃34;发票数量＆＃34 ;

--Second Query
SELECT 
CUSTOMER.CUST_NUM AS "Customer Number", 
COUNT(INVOICE.INV_NUM) AS "Number of Invoices"
FROM INVOICE
JOIN CUSTOMER ON INVOICE.CUST_NUM = CUSTOMER.CUST_NUM
GROUP BY CUSTOMER.CUST_NUM;

Customer Code Number of Invoices

     1000                  3
     1003                  2
     1001                  2
     1002                  1

如何更正First Query以使其吐出第二个查询中显示的值？

（注意：购买的cus总数是正确的，只是＆＃34;发票数量＆＃34;列错了。）

Answer 1

COUNT(DISTINCT)解决了计数问题，但您也可以通过将JOIN移到CUSTOMER表来简化查询：

SELECT i.CUST_NUM AS "Customer Number",
       COUNT(DISTINCT i.INV_NUM) AS "Number of Invoices",
       SUM(l.LINE_UNITS * l.LINE_PRICE) AS "Total Cus Purchases"
FROM INVOICE i JOIN
     LINE l
     ON i.INV_NUM = l.INV_NUMBER
GROUP BY i.CUST_NUM;

您正在使用CUST_NUM，它位于INVOICE表中。

COUNT（INVOICE.INV_NUM）在两个不同的场景中给出不同的答案

1 个答案: