SQL (Teradata)：删除由 GroupBy / CASE 语句引起的 NULL

Question

我的结果中出现 NULL 的问题。这是因为我如何将 Group By & CASE 声明与“ItemDamagedStatus”一起使用。一种解决方案可能是分解那些 CASE 语句项并对同一个表执行 JOIN。但是，当我这样做时，一些数据被丢弃了。

下面的查询实际上给了我正确的数字。我只是希望它根据以下内容汇总为一行：Product/Market/Group1。

想法？有问题吗？

SELECT   t1.Product
        , t1.Market 
        , t1.Group1                                            
        , COUNT(DISTINCT t1.ItemID ||'-'||t1.Date1) AS StoredMth
        , CASE WHEN t1.ItemDamagedStatus = 'C' THEN COUNT(DISTINCT t1.ItemID ||'-'|| t1.Date1) END AS CompleteDmgMth
        , CASE WHEN t1.ItemDamagedStatus = 'P' THEN COUNT(DISTINCT t1.ItemID ||'-'|| t1.Date1) END AS PartialDmgMth
        , CASE WHEN t1.ItemDamagedStatus = 'N' THEN COUNT(DISTINCT t1.ItemID ||'-'|| t1.Date1) END AS NotDmgMth
        , CASE WHEN t1.ItemRepairStatus = 'Y' THEN COUNT(DISTINCT t1.ItemID ||'-'|| t1.Date1) END AS RepairMth
FROM  MainDatabase.Items t1
WHERE  t1.Date1 BETWEEN '2017-01-01' AND '2017-12-31'
GROUP BY      t1.Product
            , t1.Market 
            , t1.Group1  
            , t1.ItemDamagedStatus
            , t1.ItemRepairStatus

我得到的结果：

Product Market Group1 StoredMth CompleteDmgMth PartialDmgMth NotDmgMth  RepairMth
Car     North  Y      950       50             NULL          NULL       75
Car     North  Y      NULL      NULL           100           NULL       NULL
Car     North  Y      NULL      NULL           NULL          800        NULL
Car     North  N      165       NULL           75            NULL       10
Car     North  N      NULL      NULL           NULL          90         NULL
Car     South  Y      1400      500            NULL          NULL       800
Car     South  Y      NULL      NULL           NULL          900        NULL

我想要的结果：

Product Market Group1 StoredMth CompleteDmgMth PartialDmgMth NotDmgMth  RepairMth
Car     North  Y      950       50             100           800        75
Car     North  N      165       NULL           75            90         10
Car     South  Y      1400      500            NULL          900        800

（只是一个跟进，以防万一这会让任何人失望或他们试图合并一些值......是的：CompleteDmgMth + PartialDmgMth + NotDmgMth = StoredMth，但它在我们的数据中并不是一直都非常准确，所以我们使用两种不同的方法。）

如果有些东西看起来很奇怪或框架不正确，我深表歉意，这是我第一次在这里发帖。

Answer 1

使用聚合，但不是在所有列上。您可以将CASE 表达式嵌套在COUNT(DISTINCT) 中：

SELECT t1.Product, t1.Market, t1.Group1,                                        
        COUNT(DISTINCT t1.ItemID || '-' || t1.Date1) AS StoredMth
        COUNT(DISTINCT CASE WHEN t1.ItemDamagedStatus = 'C' THEN t1.ItemID || '' || t1.Date1) END) AS CompleteDmgMth
        COUNT(DISTINCT CASE WHEN t1.ItemDamagedStatus = 'P' THEN t1.ItemID || '' || t1.Date1 END) AS PartialDmgMth
        COUNT(DISTINCT CASE WHEN t1.ItemDamagedStatus = 'N' THEN t1.ItemID || '-' || t1.Date1 END) AS NotDmgMth
        COUNT(DISTINCT CASE WHEN t1.ItemRepairStatus = 'Y' THEN t1.ItemID || '-' || t1.Date1 END) AS RepairMth
FROM  MainDatabase.Items t1
WHERE  t1.Date1 BETWEEN '2017-01-01' AND '2017-12-31'
GROUP BY t1.Product, t1.Market, t1.Group1;

Answer 2

您可以使用 MAX 仅捕获非空值，而不是对这些字段进行分组：

SELECT derived_table.Product,
derived_table.Market
, derived_table.Group1
, MAX(derived_table.StoredMth) as StoredMth
, MAX(derived_table.CompleteDmgMth) as CompleteDmgMth
, MAX(derived_table.PartialDmgMth) as PartialDmgMth
, MAX(derived_table.NotDmgMth) as NotDmgMth
, MAX(derived_table.RepairMth) as RepairMth
FROM (

SELECT   t1.Product
        , t1.Market 
        , t1.Group1                                            
        , COUNT(DISTINCT t1.ItemID ||'-'||t1.Date1) AS StoredMth
        , CASE WHEN t1.ItemDamagedStatus = 'C' THEN COUNT(DISTINCT t1.ItemID ||'-'|| t1.Date1) END AS CompleteDmgMth
        , CASE WHEN t1.ItemDamagedStatus = 'P' THEN COUNT(DISTINCT t1.ItemID ||'-'|| t1.Date1) END AS PartialDmgMth
        , CASE WHEN t1.ItemDamagedStatus = 'N' THEN COUNT(DISTINCT t1.ItemID ||'-'|| t1.Date1) END AS NotDmgMth
        , CASE WHEN t1.ItemRepairStatus = 'Y' THEN COUNT(DISTINCT t1.ItemID ||'-'|| t1.Date1) END AS RepairMth
FROM  MainDatabase.Items t1
WHERE  t1.Date1 BETWEEN '2017-01-01' AND '2017-12-31'
GROUP BY      t1.Product
            , t1.Market 
            , t1.Group1  
            , t1.ItemDamagedStatus
            , t1.ItemRepairStatus) as derived_table
GROUP BY derived_table.Product,
derived_table.Market
, derived_table.Group1;