SQL Query Combine Multiple Results

Question

Im trying to run a SQL query to display dates on 1 row instead of different rows and i also need to determine the amount of days between each date displayed.

Please find below the current query.

SELECT "Pat_Name",
    CASE WHEN "vw_Schedule"."Activity" = '123'
THEN "vw_Schedule"."App_DtTm"
ELSE NULL
END as Consult,
    CASE WHEN "vw_Schedule"."Activity" = '456'
THEN "vw_Schedule"."App_DtTm"
ELSE NULL
END as SIM,
    CASE WHEN "vw_Schedule"."Activity" = '789'
THEN "vw_Schedule"."App_DtTm"
ELSE NULL
END as PLANNING,
CASE WHEN "vw_Schedule"."SysDefStatus" = 'SC'
          THEN "vw_Schedule"."App_DtTm"
         ELSE NULL
END as TreatmentStart,
          CASE WHEN "vw_Schedule"."SysDefStatus" = 'FC'
          THEN "vw_Schedule"."App_DtTm"
       ELSE NULL   
   END as TreatmentFinished
FROM "vw_Schedule"
WHERE  "vw_Schedule"."Activity"='123' 
or "vw_Schedule"."Activity"='456'
or "vw_Schedule"."Activity"='789'
or "vw_Schedule"."SysDefStatus"='SC'
or "vw_Schedule"."SysDefStatus"='FC'

Im hoping for the output to be similar to below

Pat_Name | Consult  | Days |    SIM   | Days |  PLANNING | Days | TreatmentStart | Days |  TreatmentFinish

Test Pat | 1/9/2013 |   4  | 5/9/2013 |  10  | 15/9/2013 |  3   |    18/9/2013   |   7  |  25/9/2013

Thanks for your help.

Answer 1

If you can guarantee that there is only one row per activity per pat_Name then you can safely use an aggregate function to get the App_dtTm for each activity for each pat_name without fear of missing data. It also doesn't matter whether you use MIN or MAX if there are no duplicates.

SELECT  s.Pat_Name,
        Consult = MAX(CASE WHEN s.Activity = '123' THEN s.App_DtTm END),
        SIM = MAX(CASE WHEN s.Activity = '456' THEN s.App_DtTm END),
        PLANNING = MAX(CASE WHEN s.Activity = '789' THEN s.App_DtTm END),
        TreatmentStart = MAX(CASE WHEN s.SysDefStatus = 'SC' THEN s.App_DtTm END),
        TreatmentFinished = MAX(CASE WHEN s.SysDefStatus = 'FC' THEN s.App_DtTm END)
FROM    vw_Schedule s
WHERE   s.Activity IN ('123', '456', '789')
OR      s.SysDefStatus IN ('SC', 'FC')
GROUP BY s.Pat_Name;

If you could have duplicate dates for a single activity then it will make a difference whether you us MIN or MAX.

To get the days between activity, you can move the above query to a common table expression (or subquery if you prefer) and simply reference the columns you have created:

WITH T AS
(   SELECT  s.Pat_Name,
            Consult = MAX(CASE WHEN s.Activity = '123' THEN s.App_DtTm END),
            SIM = MAX(CASE WHEN s.Activity = '456' THEN s.App_DtTm END),
            PLANNING = MAX(CASE WHEN s.Activity = '789' THEN s.App_DtTm END),
            TreatmentStart = MAX(CASE WHEN s.SysDefStatus = 'SC' THEN s.App_DtTm END),
            TreatmentFinished = MAX(CASE WHEN s.SysDefStatus = 'FC' THEN s.App_DtTm END)
    FROM    vw_Schedule s
    WHERE   s.Activity IN ('123', '456', '789')
    OR      s.SysDefStatus IN ('SC', 'FC')
    GROUP BY s.Pat_Name
)
SELECT  Pat_Name,
        Consult,
        Days = DATEDIFF(DAY, Consult, SIM),
        SIM,
        Days = DATEDIFF(DAY, SIM, PLANNING),
        PLANNING,
        Days = DATEDIFF(DAY, PLANNING, TreatmentStart),
        TreatmentStart,
        Days = DATEDIFF(DAY, TreatmentStart, TreatmentFinish),
        TreatmentFinish
FROM    T;