sql - 连续行之间的日期差异 - 复杂

Question

我之前发布过question已得到答复，但我也需要对此进行查询。我有一个包含这样数据的表结构(日期格式为 dd/mm/yyyy)。

ID    Account Number    Unit    Admit_Date    Disch_Date
1     1001              w32     01/04/2012    
2     1002              w32     01/04/2012    01/04/2012
3     1001              ccu     03/04/2012
4     1001              w33     05/04/2012
5     1003              cicu    04/04/2012
6     1001              ccu     07/04/2012
7     1001              ccu     07/04/2012    10/04/2012
8     1003              w33     05/04/2012
9     1003              w33     05/04/2012    08/04/2012

基本上，该表涉及入住特定病房并在病房之间转移，然后最终在同一天或几天后出院的患者。查询的预期结果将是:

Account_Number                                 No. Of Days
1001              01/04/2012    03/04/2012      2
1001              03/04/2012    05/04/2012      2
1001              05/03/2012    07/04/2012      2
1001              07/04/2012    10/04/2012      3
1002              01/04/2012    01/04/2012      0
1003              04/04/2012    05/04/2012      1
1003              05/04/2012    08/04/2012      3

出院日期字段仅在患者出院时填写，因此我想计算患者每次移动日期之间的日期差，包括入院日期和出院日期。

我使用 MS Access 2003。

我希望有人能够帮助我解决这个问题。

Answer 1

过滤掉不相关的数据

对于任何复杂的查询，艺术的一部分是逐步构建查询，并进行测试。

我假设表名称是 PatientMovements 并且:

Given pairs of rows like ID = {6,7} and ID = {8,9}, it is correct to say that the row where the patient (account number), unit and admission date with null discharge date is ignored when there is also a record for the same patient, unit and admit date but a non-null discharge date.

因此，第一步是生成我们需要处理的行，从数据库中记录的表中过滤掉不相关的数据。这是两组数据的 UNION:

1. 具有非空解除日期的那些行。
2. 出院日期为空但没有相同帐户、单位和入院日期的行。

显然，UNION 的第一部分是:

SELECT * FROM PatientMovements WHERE DischargeDate IS NOT NULL

不太明显的是，UNION 的第二部分是:

SELECT *
  FROM PatientMovements AS p1
 WHERE DischargeDate IS NULL
   AND NOT EXISTS
       (SELECT *
          FROM PatientMovements AS P2
         WHERE P1.Account   = P2.Account
           AND P1.Unit      = P2.Unit
           AND P1.AdmitDate = P2.AdmitDate
           AND P2.DischargeDate IS NOT NULL
       )

现在您可以将它们合并到一个结果集中:

SELECT *
  FROM PatientMovements
 WHERE DischargeDate IS NOT NULL
UNION
SELECT *
  FROM PatientMovements AS p1
 WHERE DischargeDate IS NULL
   AND NOT EXISTS
       (SELECT *
          FROM PatientMovements AS P2
         WHERE P1.Account   = P2.Account
           AND P1.Unit      = P2.Unit
           AND P1.AdmitDate = P2.AdmitDate
           AND P2.DischargeDate IS NOT NULL
       )

您可以通过检查上面的查询是否返回 ID 为 1..5、7 和 9 的行来验证它。

警告:未经测试的代码。此答案中的 SQL 均未接近 DBMS，因此未经测试。

应用以前学到的经验教训

然后你可以应用从其他 question 学到的知识唯一的复杂之处是您必须将该查询写入两次，这很痛苦(除非 MS Access 2003 支持“WITH”子句或公用表表达式)。

<小时/>

But would there be no single query to obtain this required output?

当然，UNION 是单个查询。我想你可以这样写:

SELECT *
  FROM PatientMovements
 WHERE (DischargeDate IS NOT NULL)
    OR (DischargeDate IS     NULL
        AND NOT EXISTS
            (SELECT *
               FROM PatientMovements AS P2
              WHERE P1.Account   = P2.Account
                AND P1.Unit      = P2.Unit
                AND P1.AdmitDate = P2.AdmitDate
                AND P2.DischargeDate IS NOT NULL
            )
       )

我无法立即想到一种更紧凑的查询方式。

<小时/>

将 UNION 构建为“另一个答案”

另一个问题的接受答案有两种可能的解决方案(经评论修改并重新格式化):

SELECT T1.ID, T1.AccountNumber, T1.Date, 
       MIN(T2.Date) AS NextDate, 
       DATEDIFF("D", T1.Date, MIN(T2.Date)) AS DaysDiff
  FROM YourTable T1
  JOIN YourTable T2
    ON T1.AccountNumber = T2.AccountNumber AND T2.Date > T1.Date

或者:

SELECT ID, AccountNumber, Date, NextDate,
       DATEDIFF("D", Date, NextDate) AS DaysDiff
  FROM (SELECT ID, AccountNumber, Date,
               (SELECT MIN(Date) 
                  FROM YourTable T2
                 WHERE T2.AccountNumber = T1.AccountNumber
                   AND T2.Date > T1.Date
               ) AS NextDate
          FROM YourTable T1
        ) AS T

正如评论中所述，问题中缺少表名会导致答案中出现不同的表名；我所说的 PatientMovements 在这个答案中被称为 YourTable。另一个区别是原始问题不包括数据中的 Unit 或 DischargeDate 列。但是，我给出的 UNION 查询提供了运行这些查询的相关数据，因此剩下要做的就是将 UNION 查询写入其他答案中以代替 YourTable。这导致:

SELECT T1.ID, T1.AccountNumber, T1.Date, 
       MIN(T2.Date) AS NextDate, 
       DATEDIFF("D", T1.Date, MIN(T2.Date)) AS DaysDiff
  FROM (SELECT *
          FROM PatientMovements
         WHERE (DischargeDate IS NOT NULL)
            OR (DischargeDate IS     NULL
                AND NOT EXISTS
                    (SELECT *
                       FROM PatientMovements AS P2
                      WHERE P1.Account   = P2.Account
                        AND P1.Unit      = P2.Unit
                        AND P1.AdmitDate = P2.AdmitDate
                        AND P2.DischargeDate IS NOT NULL
                    )
               )
       ) AS T1
  JOIN (SELECT *
          FROM PatientMovements
         WHERE (DischargeDate IS NOT NULL)
            OR (DischargeDate IS     NULL
                AND NOT EXISTS
                    (SELECT *
                       FROM PatientMovements AS P2
                      WHERE P1.Account   = P2.Account
                        AND P1.Unit      = P2.Unit
                        AND P1.AdmitDate = P2.AdmitDate
                        AND P2.DischargeDate IS NOT NULL
                    )
               )
       ) AS T2
    ON T1.AccountNumber = T2.Accountnumber AND T2.Date > T1.Date

或者:

SELECT ID, AccountNumber, Date, NextDate,
       DATEDIFF("D", Date, NextDate) AS DaysDiff
  FROM (SELECT ID, AccountNumber, Date,
               (SELECT MIN(Date) 
                  FROM (SELECT *
                          FROM PatientMovements
                         WHERE (DischargeDate IS NOT NULL)
                            OR (DischargeDate IS     NULL
                                AND NOT EXISTS
                                    (SELECT *
                                       FROM PatientMovements AS P2
                                      WHERE P1.Account   = P2.Account
                                        AND P1.Unit      = P2.Unit
                                        AND P1.AdmitDate = P2.AdmitDate
                                        AND P2.DischargeDate IS NOT NULL
                                    )
                               )
                       ) AS T2
                 WHERE T2.Accountnumber = T1.AccountNumber
                   AND T2.Date > T1.Date
               ) AS NextDate
          FROM (SELECT *
                  FROM PatientMovements
                 WHERE (DischargeDate IS NOT NULL)
                    OR (DischargeDate IS     NULL
                        AND NOT EXISTS
                            (SELECT *
                               FROM PatientMovements AS P2
                              WHERE P1.Account   = P2.Account
                                AND P1.Unit      = P2.Unit
                                AND P1.AdmitDate = P2.AdmitDate
                                AND P2.DischargeDate IS NOT NULL
                            )
                       )
               ) AS T1
        ) AS T

因此，只要您小心，并在片段中开发查询，然后将它们一致地组合起来，就可以驯服看起来最糟糕的查询。

通用表表达式

请注意，SQL 标准具有“公用表表达式”(CTE)，又名“WITH 子句”，这可以使事情变得更容易。

WITH YourTable AS
   (SELECT *
      FROM PatientMovements
     WHERE (DischargeDate IS NOT NULL)
        OR (DischargeDate IS     NULL
            AND NOT EXISTS
                (SELECT *
                   FROM PatientMovements AS P2
                  WHERE P1.Account   = P2.Account
                    AND P1.Unit      = P2.Unit
                    AND P1.AdmitDate = P2.AdmitDate
                    AND P2.DischargeDate IS NOT NULL
                )
           )
     )
SELECT T1.ID, T1.AccountNumber, T1.Date, 
       MIN(T2.Date) AS NextDate, 
       DATEDIFF("D", T1.Date, MIN(T2.Date)) AS DaysDiff
  FROM YourTable T1
  JOIN YourTable T2
    ON T1.AccountNumber = T2.AccountNumber AND T2.Date > T1.Date

或者:

WITH YourTable AS
   (SELECT *
      FROM PatientMovements
     WHERE (DischargeDate IS NOT NULL)
        OR (DischargeDate IS     NULL
            AND NOT EXISTS
                (SELECT *
                   FROM PatientMovements AS P2
                  WHERE P1.Account   = P2.Account
                    AND P1.Unit      = P2.Unit
                    AND P1.AdmitDate = P2.AdmitDate
                    AND P2.DischargeDate IS NOT NULL
                )
           )
     )
SELECT ID, AccountNumber, Date, NextDate,
       DATEDIFF("D", Date, NextDate) AS DaysDiff
  FROM (SELECT ID, AccountNumber, Date,
               (SELECT MIN(Date) 
                  FROM YourTable T2
                 WHERE T2.AccountNumber = T1.AccountNumber
                   AND T2.Date > T1.Date
               ) AS NextDate
          FROM YourTable T1
        ) AS T

使用 CTE 的主要优点之一是，优化器被明确告知表表达式在所有使用的地方都是相同的，而当它被多次写出时，它可能无法发现这种共性。另外，多次编写查询可能会导致两个“本应相同”的查询实际上由于编辑错误而略有不同； CTE 排除了这种可能性。当前环境下的另一个优势是，将 CTE 与其他问题的解决方案结合起来简直就是 child 子的游戏。

遗憾的是，MS Access 2003 不太可能支持 CTE。我分担你的痛苦；我使用的 DBMS 主要也没有。