Oracle SQL 如何在连接期间计算列值出现次数和 Group BY答案

【问题标题】：Oracle SQL How to Count Column Value Occurences and Group BY during joinsOracle SQL 如何在连接期间计算列值出现次数和 Group BY
【发布时间】：2019-05-17 10:05:28
【问题描述】：

我正在处理另一个 SQL 查询，尝试在进行计数和连接表的同时对一组记录进行分组。有关用于构建和填充表的目标、当前查询和附加脚本，请参见下文。

显示查看的书籍多于 DVD 的所有客户。展示客户姓名、图书结账总数和 DVD 结账总数。种类按客户名字和姓氏排列的结果。

SELECT C.CUSTOMER_FIRSTNAME, C.CUSTOMER_LASTNAME, COUNT(T.TRANSACTION_ID)
FROM customer C
INNER JOIN library_card LC ON C.CUSTOMER_ID = LC.CUSTOMER_ID
INNER JOIN transaction T ON LC.LIBRARY_CARD_ID = T.LIBRARY_CARD_ID
INNER JOIN physical_item P ON T.PHYSICAL_ITEM_ID = P.PHYSICAL_ITEM_ID
INNER JOIN catalog_item CT ON P.CATALOG_ITEM_ID = CT.CATALOG_ITEM_ID 
GROUP BY C.CUSTOMER_FIRSTNAME, C.CUSTOMER_LASTNAME
ORDER BY C.CUSTOMER_FIRSTNAME, C.CUSTOMER_LASTNAME;

先运行：https://drive.google.com/open?id=1PYAZV4KIfZtxP4eQn35zsczySsxDM7ls

第二次运行：https://drive.google.com/open?id=1pAzWmJqvD3o3n6YJqVUM6TtxDafKGd3f

编辑
在巴巴罗斯先生的帮助下，我提出了以下查询，该查询更接近。但是，这个查询没有返回任何 DVD 的结果，这让我相信这是一个连接问题。

SELECT C.CUSTOMER_FIRSTNAME, C.CUSTOMER_LASTNAME, COUNT(CT1.TYPE) AS BOOK_COUNT, COUNT(CT2.TYPE) AS DVD_COUNT
FROM customer C
INNER JOIN library_card LC ON C.CUSTOMER_ID = LC.CUSTOMER_ID
INNER JOIN transaction T ON LC.LIBRARY_CARD_ID = T.LIBRARY_CARD_ID
INNER JOIN physical_item P ON T.PHYSICAL_ITEM_ID = P.PHYSICAL_ITEM_ID
INNER JOIN catalog_item CT1 ON P.CATALOG_ITEM_ID = CT1.CATALOG_ITEM_ID AND CT1.TYPE = 'BOOK'
LEFT OUTER JOIN catalog_item CT2 ON P.CATALOG_ITEM_ID = CT2.CATALOG_ITEM_ID AND CT2.TYPE = 'DVD'
GROUP BY C.CUSTOMER_FIRSTNAME, C.CUSTOMER_LASTNAME, CT1.TYPE, CT2.TYPE
ORDER BY C.CUSTOMER_FIRSTNAME, C.CUSTOMER_LASTNAME;

【问题讨论】：

标签： sql oracle join oracle11g group-by

【解决方案1】：

您可以使用 catalog_item 表两次（将书籍和 dvd 视为单独的表），并通过 HAVING 子句进行比较：

SELECT C.CUSTOMER_FIRSTNAME, C.CUSTOMER_LASTNAME, 
       COUNT(CT1.CATALOG_ITEM_ID) as "Book Checkout", 
       COUNT(CT2.CATALOG_ITEM_ID) as "DVD Checkout"
  FROM customer C
 INNER JOIN library_card LC ON C.CUSTOMER_ID = LC.CUSTOMER_ID
 INNER JOIN transaction T ON LC.LIBRARY_CARD_ID = T.LIBRARY_CARD_ID
 INNER JOIN physical_item P ON T.PHYSICAL_ITEM_ID = P.PHYSICAL_ITEM_ID
  LEFT JOIN catalog_item CT1 ON P.CATALOG_ITEM_ID = CT1.CATALOG_ITEM_ID AND CT1.TYPE = 'BOOK'
  LEFT JOIN catalog_item CT2 ON P.CATALOG_ITEM_ID = CT2.CATALOG_ITEM_ID AND CT1.TYPE = 'DVD'
 GROUP BY C.CUSTOMER_FIRSTNAME, C.CUSTOMER_LASTNAME
HAVING COUNT(CT1.CATALOG_ITEM_ID) > COUNT(CT2.CATALOG_ITEM_ID)
 ORDER BY C.CUSTOMER_FIRSTNAME, C.CUSTOMER_LASTNAME;

CUSTOMER_FIRSTNAME  CUSTOMER_LASTNAME   Book Checkout  DVD Checkout
------------------  -----------------   -------------  -------------
Deena               Pilgrim                   3              1
Emile               Cross                     5              2

【讨论】：

这个查询没有返回任何记录：/
我稍微修改了查询以获取一些记录，但是 CT1 和 CT2 表的连接以某种方式关闭。我无法同时返回 DVD 和书籍的准确记录。请参阅更新的问题。谢谢。
@RyanCohan 不客气。好的，我解决了问题，抱歉，问题是由于inner 加入了新添加的条件，这些条件应该是left。

【解决方案2】：

请尝试删除您的 group by 子句中的 ,CT1.TYPE, CT2.TYPE。

【讨论】：

【解决方案3】：

使用“条件聚合”（在聚合函数中使用 case 表达式）

SELECT
    C.CUSTOMER_FIRSTNAME
  , C.CUSTOMER_LASTNAME
  , COUNT( CASE WHEN CT.TYPE = 'BOOK' THEN T.TRANSACTION_ID END ) books
  , COUNT( CASE WHEN CT.TYPE = 'DVD' THEN T.TRANSACTION_ID END ) dvds
FROM customer C
INNER JOIN library_card LC ON C.CUSTOMER_ID = LC.CUSTOMER_ID
INNER JOIN transaction T ON LC.LIBRARY_CARD_ID = T.LIBRARY_CARD_ID
INNER JOIN physical_item P ON T.PHYSICAL_ITEM_ID = P.PHYSICAL_ITEM_ID
INNER JOIN catalog_item CT ON P.CATALOG_ITEM_ID = CT.CATALOG_ITEM_ID
GROUP BY
    C.CUSTOMER_FIRSTNAME
  , C.CUSTOMER_LASTNAME
HAVING
     COUNT( CASE WHEN CT.TYPE = 'BOOK' THEN T.TRANSACTION_ID END ) 
   > COUNT( CASE WHEN CT.TYPE = 'DVD' THEN T.TRANSACTION_ID END )
ORDER BY
    C.CUSTOMER_FIRSTNAME
  , C.CUSTOMER_LASTNAME
;

【讨论】：