Question

我有一些数据：

Declare @table table (RID VARCHAR(10),
                      CommType INT,
                      CommunicationType INT,
                      VALUE VARCHAR(20),
                      lastDate Datetime)

INSERT INTO @table (RID, CommType, CommunicationType, VALUE, lastDate) 
VALUES 
('00WAAS', 3, 0, 'mohan@gmail', '2012-06-15 15:23:49.653'),
('00WAAS', 3, 1, 'manasa@gmail', '2015-08-15 15:23:49.653'),
('00WAAS', 3, 2, 'mother@gmail', '2014-09-15 15:23:49.653'),
('00WAAS', 3, 2, 'father@gmail', '2016-01-15 15:23:49.653'),
('00WAAS', 3, 0, 'hello@gmail', '2013-01-15 15:23:49.653')

我的查询：

SELECT 
    TT.RID,
    COALESCE(Homemail, BusinessMail, OtherMail) Mail  
FROM 
    (SELECT
         RID, MAX(Homemail) Homemail,
         MAX(BusinessMail) BusinessMail,
         MAX(OtherMail) OtherMail 
     FROM 
         (SELECT
              RID, 
              CASE 
                 WHEN CommType = 3 AND CommunicationType = 0 THEN VALUE 
              END AS Homemail,
              CASE 
                 WHEN CommType = 3 AND CommunicationType = 1 THEN VALUE 
              END AS BusinessMail,
              CASE 
                 WHEN CommType = 3 AND CommunicationType = 2 THEN VALUE 
              END AS OtherMail,
              lastDate
          FROM
              @table) T
      GROUP BY RID) TT

我期待的是什么

这里我需要获得结果CommType = 3 and CommunicationType = 0然后根据最新日期和数据不可用的相关值 CommType = 3且CommunicationType = 0

然后我需要获取CommunicationType = 1的数据基于最新日期的相关值，如果没有数据 CommunicationType = 1

然后CommunicationType = 2，基于该CommunicationTypes的最新日期。

这里我尝试了Case condition，MAX和Coalesce

如果在CommunicationType = 0中存在组合数据，则根据最新日期获取CommunicationType = 0

如果CommunicationType = 0中不存在组合数据，则根据最新日期

获取CommunicationType = 1

如果CommunicationType = 1中不存在组合数据，则根据最新日期

获取CommunicationType = 2

Answer 1

如果我理解正确，请使用ROW_NUMBER()：

SELECT tt.RID,COALESCE(tt.Homemail,tt.businessMail,tt.OtherMail) 
FROM(
    select s.RID,
        MAX(CASE WHEN s.CommType = 3 AND s.CommunicationType = 0 THEN s.VALUE END) AS Homemail,
        MAX(CASE WHEN s.CommType = 3 AND s.CommunicationType = 1 THEN s.VALUE END) AS BusinessMail,
        MAX(CASE WHEN s.CommType = 3 AND s.CommunicationType = 2 THEN s.VALUE END) AS OtherMail
     from (SELECT t.*,ROW_NUMBER() OVER(PARTITION BY t.rid,t.communicationType ORDER BY t.lastDate DESC)
           FROM @table t
           WHERE t.commType = 3) s
    WHERE s.rnk = 1
    GROUP BY s.rid) tt

Answer 2

我不完全确定我已理解这一要求。但我想你想要：

为每个RID返回一条记录。
返回的记录的CommType应为3。
如果有多个CommType 3的记录，您希望记录的CommunicationType最低。
如果还有多条记录，您希望使用最新的记录lastDate。

此查询使用windowed function ROW_NUMBER对子查询中的可用记录进行排名。 PARTITION BY确保每个RID都是单独排名的。外部查询返回排名为1的所有记录。

<强>查询

SELECT
    r.*
FROM
    (           
        /* For each RID We want the lowest communication type with 
         * the most recent last date.
         */
        SELECT
            ROW_NUMBER() OVER (PARTITION BY RID ORDER BY CommunicationType, lastDate DESC) AS rn,
            *
        FROM
            @table
        WHERE
            CommType = 3
    ) AS r
WHERE
    r.rn = 1
;

后续步骤

这个查询还可以，但可能更好。例如，如果两个记录匹配CommType，CommunicationType和lastDate，会发生什么？阅读ROW_NUMBER，RANK，DENSE_RANK和NTILE之间的差异将有助于您在此处找出您的选择。

如何根据Case条件和MAX Date获取数据

2 个答案: