Temporarily replacing values in SQL or subbing in values via SQL

Question

I'm new to SQL and dont think I truly grasp it fully.

My second selected item,after date, gives me (∑r*mv)/(∑mv) which is the weighted returns of the portfolio. The next two SUM columns are attempt to weight the returns based on my selected values.

SELECT 
date, 
Sum(mv*retmtd)/Sum(mv),

SUM(DISTINCT retmtd*
        CASE asset
        WHEN 'SP500' then 200000
        WHEN 'UST2' then 200000
        WHEN 'FTSE' then 600000
        END)/1000000,

SUM( retmtd*
        CASE 
        WHEN asset ='SP500' AND mv IS NOT NULL then 200000
        WHEN asset ='UST2' AND mv IS NOT NULL then 200000
        WHEN asset ='FTSE' AND mv IS NOT NULL then 600000
        END)/
      SUM(  CASE 
        WHEN asset ='SP500' AND mv IS NOT NULL then 200000
        WHEN asset ='UST2' AND mv IS NOT NULL then 200000
        WHEN asset ='FTSE' AND mv IS NOT NULL then 600000
        END) 

FROM [dbo].[AssetRet]

WHERE
asset IN ('SP500','UST2','FTSE')
AND
date >=  '12/31/2000' 

Is there anyway that I change set the value of mv manually (to say 200000) over the lifetime so I can see how different weighted portfolios would have performed. This is supposed to be dynamic and reusable so going creating a new column in the database is unfeasible if I want to do this over and over. None of my SQL attempts seems to get the correct answer.

The purpose of this exercise is to create synthetic portfolios that would show how a portfolio would have performed if different weights had been given to different asset classes during their life in the portfolio. I hope this makes sense.

e.g instead of mv (market value of the position) being used to weigh that asset in the portfolio I would use a static hypothesized value (200000)

This table is what Sum(mv*retmtd)/Sum(mv) returns which is correct

Date      SP500     UST2     FTSE     MV     MV     MV       RESULT
3/31/10   0.34                        19878                  0.34
6/30/10   -0.11     0.12              19954  840712          0.116
6/30/13   -0.48     -1.30    -0.76    9914   934892 384193   -1.135

And this what I want the other querys to retrieve

Date      SP500     UST2     FTSE     MV     MV     MV       RESULT
3/31/10   0.34                        200000                 0.34
6/30/10   -0.11     0.12              200000 200000          0.006
6/30/13   -0.48     -1.30    -0.76    200000 200000 600000   -0.809

Is there a way to do this via SQL?

Answer 1

I found a solution to this problem that may be of use to anyone that stumbles across this question.

By wrapping it in another query and using just a case statement in the wrapped query you can modify the data and then do the required data calculations...

SELECT 
x.date, 
Sum(x.hyp_mv* x.retmtd)/Sum(x.hyp_mv) as weightedreturns

FROM

    (
    SELECT 
    date,
    asset,
    retmtd,

    (CASE asset
     WHEN 'SP500' then 200000
     WHEN 'UST2' then 200000
     WHEN 'FTSE' then 600000
     END) as hyp_mv

    FROM [dbo].[AssetRet]

    WHERE
    asset IN ('SP500','UST2','FTSE')
    AND
    date >=  '12/31/2000' 
    )x

GROUP BY
x.date

ORDER BY
x.date

Answer 2

enter code hereIs there any way to set the value of mv manually to 200000...

Yes -- type 200000 instead of mv

Are you thinking about a parameter maybe?

i.e.:

        DECLARE @mv_ftse int
        DECLARE @mv_ust2 int
        DECLARE @mv_sp500 int
        SET @mv_ftse = 600000
        SET @mv_ust2 = 200000
        SET @mv_sp500 = 200000

    SELECT 
    date, 
    Sum(mv*retmtd)/Sum(mv),

    SUM(DISTINCT retmtd*
        CASE asset
        WHEN 'SP500' then @mv_sp500
        WHEN 'UST2' then @mv_ust2
        WHEN 'FTSE' then @mv_ftse
        END)/1000000,
...