Question

I am trying to write a query that would select data from multiple lines depending if there is a newer value. This has been giving me headaches for a long time already. The table is structured this way:

UniqID ProblemID  DateTime   Status PersonID ResponsibleID ActionID Comment  Deadline    PartID
15589   15589    01/16 12:11   0       25         48          12      bla1   01/16 12:11  T9865
15592   15589    01/16 12:25   1       48         48          105     bla2   null         null
15601   15589    01/16 13:08   3       56         null        195     bla3   null         N2654
15641   15589    01/17 18:02   3       11         23          35      null   01/18 15:00  null
15705   15589    01/18 10:24   5       23         null        255     bla4   null         null

This is a mistake log and I need to perform several slightly different queries on this data.

• e.g. if person 48 was involved with this mistake (15589) as PersonID or as ResponsibleID.

This query would have to return

    ProblemID (first)DateTime (last)Status (first)Person (last)Responsible (last)action (first)Comment (last)deadline (last)PartID        
      15589      01/16 12:11       5            25            23                255         bla1        01/18 15:00      N2654

• e.g show all mistakes for the last 24hours
• e.g show all mistakes where PartID T9865 was involved

I have made several attempts at this query, but the best that came out was a query that selects all stuff from the last line or the first one. I am actually struggling to figure out how to select the (last)ResponsibleID if it is not contained in the last line. The same for other columns obviously. The only solution I can think of right now is a simple select that would return me all the rows and just filter that necessary data in a foreach loop with PHP. Because selecting different values in multiple lines is just beyond my skill 🙂

Thanks in advance

Answer 1

The only solution I can think of is to repeat the conditions in subselects. I see no other way to get to the first/last column values that are NOT NULL.

SQL Statement

;WITH CurrentProblemID AS (
  SELECT  DISTINCT ProblemID
  FROM    Mistakes 
  WHERE   PersonID = 48 
          OR ResponsibleID = 48
)

SELECT  [ProblemID] = cpi.ProblemID
        , [(first) DateTime] = (SELECT MIN(DateTime) FROM Mistakes WHERE ProblemID = cpi.ProblemID AND DateTime IS NOT NULL)
        , [(last) Status] = (SELECT Status FROM Mistakes WHERE DateTime = (SELECT MAX(DateTime) FROM Mistakes WHERE ProblemID = cpi.ProblemID AND Status IS NOT NULL))
        , [(first) Person] = (SELECT PersonID FROM Mistakes WHERE DateTime = (SELECT MIN(DateTime) FROM Mistakes WHERE ProblemID = cpi.ProblemID AND PersonID IS NOT NULL))
        , [(last) Responsible] = (SELECT ResponsibleID FROM Mistakes WHERE DateTime = (SELECT MAX(DateTime) FROM Mistakes WHERE ProblemID = cpi.ProblemID AND ResponsibleID IS NOT NULL))
        , [(last) Action] = (SELECT ActionID FROM Mistakes WHERE DateTime = (SELECT MAX(DateTime) FROM Mistakes WHERE ProblemID = cpi.ProblemID AND ActionID IS NOT NULL))
        , [(first) Comment] = (SELECT Comment FROM Mistakes WHERE DateTime = (SELECT MIN(DateTime) FROM Mistakes WHERE ProblemID = cpi.ProblemID AND Comment IS NOT NULL))
        , [(last) Deadline] = (SELECT Deadline FROM Mistakes WHERE DateTime = (SELECT MAX(DateTime) FROM Mistakes WHERE ProblemID = cpi.ProblemID AND Deadline IS NOT NULL))
        , [(last) PartID] = (SELECT PartID FROM Mistakes WHERE DateTime = (SELECT MAX(DateTime) FROM Mistakes WHERE ProblemID = cpi.ProblemID AND PartID IS NOT NULL))
FROM    CurrentProblemID cpi

Test script

;WITH Mistakes AS (
  SELECT  *
  FROM    ( 
            VALUES
              (15589, 15589, '01/16 12:11', 0, 25, 48, 12, 'bla1', '01/16 12:11', 'T9865')
              , (15592, 15589, '01/16 12:25', 1, 48, 48, 105, 'bla2', null, null)
              , (15601, 15589, '01/16 13:08', 3, 56, null, 195, 'bla3', null, 'N2654')
              , (15641, 15589, '01/17 18:02', 3, 11, 23, 35, null, '01/18 15:00', null)
              , (15705, 15589, '01/18 10:24', 5, 23, null, 255, 'bla4', null, null)
          ) AS v (UniqID, ProblemID, DateTime, Status, PersonID, ResponsibleID, ActionID, Comment, Deadline, PartID)
)          
, CurrentProblemID AS (
  SELECT  DISTINCT ProblemID
  FROM    Mistakes 
  WHERE   PersonID = 48 
          OR ResponsibleID = 48
)

SELECT  [ProblemID] = cpi.ProblemID
        , [(first) DateTime] = (SELECT MIN(DateTime) FROM Mistakes WHERE ProblemID = cpi.ProblemID AND DateTime IS NOT NULL)
        , [(last) Status] = (SELECT Status FROM Mistakes WHERE DateTime = (SELECT MAX(DateTime) FROM Mistakes WHERE ProblemID = cpi.ProblemID AND Status IS NOT NULL))
        , [(first) Person] = (SELECT PersonID FROM Mistakes WHERE DateTime = (SELECT MIN(DateTime) FROM Mistakes WHERE ProblemID = cpi.ProblemID AND PersonID IS NOT NULL))
        , [(last) Responsible] = (SELECT ResponsibleID FROM Mistakes WHERE DateTime = (SELECT MAX(DateTime) FROM Mistakes WHERE ProblemID = cpi.ProblemID AND ResponsibleID IS NOT NULL))
        , [(last) Action] = (SELECT ActionID FROM Mistakes WHERE DateTime = (SELECT MAX(DateTime) FROM Mistakes WHERE ProblemID = cpi.ProblemID AND ActionID IS NOT NULL))
        , [(first) Comment] = (SELECT Comment FROM Mistakes WHERE DateTime = (SELECT MIN(DateTime) FROM Mistakes WHERE ProblemID = cpi.ProblemID AND Comment IS NOT NULL))
        , [(last) Deadline] = (SELECT Deadline FROM Mistakes WHERE DateTime = (SELECT MAX(DateTime) FROM Mistakes WHERE ProblemID = cpi.ProblemID AND Deadline IS NOT NULL))
        , [(last) PartID] = (SELECT PartID FROM Mistakes WHERE DateTime = (SELECT MAX(DateTime) FROM Mistakes WHERE ProblemID = cpi.ProblemID AND PartID IS NOT NULL))
FROM    CurrentProblemID cpi