SQL Server query assistance needed

问题

I'm storing a bunch of data in a view (converted MS Access queries to views). Now what I'm trying to do is write a stored procedure to pull data based on when the data was added. Here is the query that I'm running

Select 
    Name, PlanID, ApptDate, 1stAppt, rn, 
from 
    (Select 
         *,   
         row_number() over (partition by PlanID Order BY AddedonDate desc) as rn 
     From vClientInfo)

So this pulls all my data okay. The issue that I have to address is, the client actually comes in for the 1st appt and 2nd appt - Basically I need to pull the data for LATEST date, as well as EARLIEST, and include a '2ndAppt' in my query. So 1stAppt and 2ndAppt hold a string value that I will later use...The 2 values might differ from 1stAppt to 2ndAppt - and only AddedOn date will tell me if there was a different (earliest for 1stAppt, and latest for 2ndAppt).

Select 
    Name, PlanID, ApptDate, 1stAppt, 2ndAppt rn, 
From 
    (Select 
         *, 
         row_number() over (partition by PlanID Order BY AddedonDate desc) as rn 
     From  vClientInfp)

So I did this and I changed this...

(Select *,  row_number() over (partition by PlanID Order BY AddedonDate *ASC*)

However I'm not sure if this is pulling correct data as I'm working with a lot of data and hard to verify. So basically I need to do a union so that both my queries pull in the correct data. Originally I was getting 1920 records, so with a union i should be getting just as many too i assume, however, the number is double so 3840, why?

Select 
    Name, PlanID, ApptDate, 1stAppt, 2ndappt, rn, 
From 
    (Select 
         *,   
         row_number() over (partition by PlanID Order BY AddedonDate desc) as rn 
     From  vClientInfo

     Union All

     Select 
         Name, PlanID, ApptDate, 1stAppt, 2ndAppt, rn, 
     From 
         (Select 
              *,  
              row_number() over (partition by PlanID Order BY AddedonDate asc) as rn 
          From vClientInfo

回答1:

You are using window function, but you are not filtering by it, so whats the point? If you want the earliest and the latest, choose rn = 1 :

Select Name, PlanID, ApptDate, 1stAppt,2ndappt, rn,
from (Select *,
            row_number() over (partition by PlanID Order BY AddedonDate desc) as rn
     from  vClientInfo
     Union All
     Select *, 
           row_number() over (partition by PlanID Order BY AddedonDate asc) as rn 
     from  vClientInfo)
WHERE rn = 1

If you want 1st appt from the earliest and 2ndappt from the latest :

Select Name, PlanID, ApptDate,
       MAX(CASE WHEN rnk = 1 then 1stAppt end) as 1stAppt,
       MAX(CASE WHEN rn = 1 THEN 2ndappt end) as 2ndAppt
from (Select *,
            row_number() over (partition by PlanID Order BY AddedonDate desc) as rn,
     0 as rnk
     from  vClientInfo
     Union All
     Select *,
           0 as rn,
           row_number() over (partition by PlanID Order BY AddedonDate asc) as rnk 
     from  vClientInfo)
GROUP BY Name,PlanID,ApptDate

来源：https://stackoverflow.com/questions/36065933/sql-server-query-assistance-needed

标签

sql

sql-server

select

union

union-all