Sql 根据最新日期从三个表中选择一条记录

我在SQL Server 2012中有一个具有唯一TransactionID的TransactionMaster表。LowTransaction、MediumTransaction和HighTransaction表中将提供相同的TransactionID

对于TransactionMaster中的每个TransactionID，我需要显示一条StatusMessage。StatusMessage可能来自3个表中的任何一个-基于

CRTDTEC

和

CRTTIME

列中规定的日期

在SQL Server 2012中，选择与最新日期对应的StatusMessage的最佳方法是什么

注：CRTDTEC格式-

YYMMDD

和CRTTIME格式-

HHMMSS

代码

DECLARE @TransactionMaster TABLE (TransactionID INT)

DECLARE @LowTransaction TABLE (TransactionID INT, StatusMessage VARCHAR(80), CRTDTEC VARCHAR(8), CRTTIME VARCHAR(6))
DECLARE @MediumTransaction TABLE (TransactionID INT, StatusMessage VARCHAR(80), CRTDTEC VARCHAR(8), CRTTIME VARCHAR(6))
DECLARE @HighTransaction TABLE (TransactionID INT, StatusMessage VARCHAR(80), CRTDTEC VARCHAR(8), CRTTIME VARCHAR(6))

INSERT INTO @TransactionMaster VALUES (1)
INSERT INTO @TransactionMaster VALUES (2)
INSERT INTO @TransactionMaster VALUES (3)

INSERT INTO @LowTransaction VALUES (1,'1  Low','20131213','235959')
INSERT INTO @MediumTransaction VALUES (1,'1','20131213','235900')
INSERT INTO @HighTransaction VALUES (1,'1 High','20111213','235959')

INSERT INTO @LowTransaction VALUES (2,'2  Low','20111213','235959')

INSERT INTO @LowTransaction VALUES (3,'3 Low','20111213','235959')
INSERT INTO @MediumTransaction VALUES (3,'3 Medium','20111213','235959')
INSERT INTO @HighTransaction VALUES (3,'3 High','20140101','235959')

预期结果

(1,'1  Low','20131213','235959')
(2,'2  Low','20111213','235959')
(3,'3 High','20140101','235959')

TransactionID   StatusMessage  CRTDTEC    CRTTIME
1               1  Low         20131213   235959
2               2  Low         20111213   235959
3               3 High         20140101   235959

---

最简单的方法可能是

WITH TransConsolidated
     AS (SELECT *
         FROM   @LowTransaction
         UNION ALL
         SELECT *
         FROM   @MediumTransaction
         UNION ALL
         SELECT *
         FROM   @HighTransaction)
SELECT TM.TransactionID,
       CA.*
FROM   @TransactionMaster TM
       CROSS APPLY (SELECT TOP 1 *
                    FROM   TransConsolidated TC
                    WHERE  TC.TransactionID = TM.TransactionID
                    ORDER  BY CRTDTEC DESC,
                              CRTTIME DESC) CA 

或者另一种可能性（如果所有表上都有一个按

TransactionID

排序的覆盖索引）是合并并连接所有涉及的四个表

;WITH CTE
     AS (SELECT TM.TransactionID,
                MAX(CA.CRTDTEC + CA.CRTTIME + CA.StatusMessage) AS MaxRow
         FROM   @TransactionMaster TM
                LEFT MERGE JOIN @LowTransaction LT
                  ON LT.TransactionID = TM.TransactionID
                LEFT MERGE JOIN @MediumTransaction MT
                  ON MT.TransactionID = TM.TransactionID
                LEFT MERGE JOIN @HighTransaction HT
                  ON HT.TransactionID = TM.TransactionID
                CROSS APPLY (SELECT LT.*
                             UNION ALL
                             SELECT MT.*
                             UNION ALL
                             SELECT HT.*) CA
         GROUP  BY TM.TransactionID)
SELECT TransactionID,
       SUBSTRING(MaxRow, 1, 8),
       SUBSTRING(MaxRow, 9, 6),
       SUBSTRING(MaxRow, 16, 80)
FROM   CTE 

---

我想你可以这样做

SELECT TransactionID, StatusMessage, CRTDTEC,   CRTTIME  
FROM
  (
    SELECT *, rn =  ROW_NUMBER() OVER (PARTITION BY TransactionID ORDER BY CRTDTEC DESC) 
    FROM 
    (
    SELECT *    FROM @LowTransaction
    UNION ALL
    SELECT *    FROM @MediumTransaction
    UNION ALL
    SELECT *    FROM @HighTransaction
    )q
  ) q2
WHERE rn = 1

结果集

(1,'1  Low','20131213','235959')
(2,'2  Low','20111213','235959')
(3,'3 High','20140101','235959')

TransactionID   StatusMessage  CRTDTEC    CRTTIME
1               1  Low         20131213   235959
2               2  Low         20111213   235959
3               3 High         20140101   235959

---

所有4个表中有多少行？

TransactionID

在这四个方面都是唯一的吗？还有，为什么要将日期和时间存储为字符串而不是

date

和

time

？@MartinSmith目前TransactionID在这四个方面都是唯一的。但我希望看到一个解决方案，即使不是这样。。。这是一个我无法更改的现有数据库。。我刚刚演示了如何使用表变量。。。