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% change between rows

I want to get something like the following.

week count % changed
10   100     0
11   200     100%
12   300     50%
13   100     -66.7%
14   500     500%


What's the simplest way to do this?
0
gotaquestion
Asked:
gotaquestion
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1 Solution
 
Scott PletcherSenior DBACommented:
Perhaps something like this:

SELECT week, [count],
    (SELECT ISNULL(CAST((currwk.[count] - prevwk.[count]) AS DECIMAL(10,2)) /
            CAST(currwk.[count] AS DECIMAL(10,2)) * 100.00,0) AS '% changed'
     FROM tablename prevwk
     WHERE prevwk.week = currwk.week - 1)
FROM tablename currwk
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spcmnspffCommented:
This will find the percentage change in records. in a table provided there is a column named week.  Change Column1 to the name of any field in the table other than Week.

SET ARITHABORT OFF
Select [Week], C1 [Count], (C1-C2)/C1 [% Change]
From
     (select T1.[Week], Count(T1.Column1) C1,
         (Select IsNull(Count(T2.Column1) from MyTable T2 Where T2.[Week] = T1.[Week]-1),0) C2
     From MyTable T1
     Group By T1.[Week]) VT


If you don't have a week field, then you can use the datepart function to get the date from a create date:


SET ARITHABORT OFF
Select [Week], C1 [Count], (C1-C2)/C2 [% Change]
From
     (select DatePart(wk,T1.CreateDt) [Week],
         Count(T1.Column1) C1,
         (Select IsNull(Count(T2.Column1)
             from MyTable T2
             Where DatePart(wk,T2.CreateDt) =
                 DatePart(wk,T1.CreateDt)-1),0) C2
      From MyTable T1
      Group By DatePart(wk,T1.CreateDt)-1)) VT


0
 
spcmnspffCommented:
Minor Change:  Had to divide by C2 rather than C1:

SET ARITHABORT OFF
Select [Week], C1 [Count], (C1-C2)/C2 [% Change]
From
    (select T1.[Week], Count(T1.Column1) C1,
        (Select IsNull(Count(T2.Column1) from MyTable T2 Where T2.[Week] = T1.[Week]-1),0) C2
    From MyTable T1
    Group By T1.[Week]) VT


Or with the datepart function:

SET ARITHABORT OFF
Select [Week], C1 [Count], (C1-C2)/C2 [% Change]
From
    (select DatePart(wk,T1.CreateDt) [Week],
        Count(T1.Column1) C1,
        (Select IsNull(Count(T2.Column1)
            from MyTable T2
            Where DatePart(wk,T2.CreateDt) =
                DatePart(wk,T1.CreateDt)-1),0) C2
     From MyTable T1
     Group By DatePart(wk,T1.CreateDt)-1)) VT
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gotaquestionAuthor Commented:
I've created a table to support your queries and with both the last ones your proposed I'm getting.  

Server: Msg 156, Level 15, State 1, Line 7
Incorrect syntax near the keyword 'from'.

I think it's missing a )

I can't seem to see it.


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spcmnspffCommented:
Oops.  Fixed it.  I had to change the  postition of my isnull =)  :

SET ARITHABORT OFF
Select [Week], C1 [Count], (C1-C2)/C2 [% Change]
From
   (select T1.[Week], Count(T1.Column1) C1,
       IsNull((Select Count(T2.Column1) from MyTable T2 Where T2.[Week] = T1.[Week]-1),0) C2
   From MyTable T1
   Group By T1.[Week]) VT


Or with the datepart function:

SET ARITHABORT OFF
Select [Week], C1 [Count], (C1-C2)/C2 [% Change]
From
   (select DatePart(wk,T1.CreateDt) [Week],
       Count(T1.Column1) C1,
       IsNull((Select Count(T2.Column1)
           from MyTable T2
           Where DatePart(wk,T2.CreateDt) =
               DatePart(wk,T1.CreateDt)-1),0) C2
    From MyTable T1
    Group By DatePart(wk,T1.CreateDt)) VT
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gotaquestionAuthor Commented:
Thanks, I had to fix the divide by zero error because the
SET ARITHIGNORE OFF
SET ARITHABORT OFF
were not working for some reason.

Select [Week], C1 [Count], CASE C2 WHEN 0 THEN 0 ELSE (C1-C2)/C2 END [% Change]
From
  (select T1.[Week], sum(T1.Column1) C1,
      IsNull((Select sum(T2.Column1) from MyTable T2 Where T2.[Week] = T1.[Week]-1),0) C2
  From MyTable T1
  Group By T1.[Week]) VT
0

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