Question

A SQL Table (Trades) has three fields AvgProfit, MinProfit and Hold – Hold is a Computed Colum…

If AvgProfit < MinProfit, Hold = ‘Hold’ and if AvgProfit > MinProfit, Hold = ‘Trade’
The Computed Col formula for Hold is as follows.

 SQL Table Trades
 AvgProfit varchar(35)
 MinProfit varchar(35)
 Hold varchar(35)


 (case when CONVERT([decimal](8,4),isnull([AvgProfit],(0)),(0))>=CONVERT([decimal](8,4),isnull([MinProfit],(0)),(0)) then 'Trade' else 'Hold' end)

PROBLEM: Updates cause the AvgProfit to be empty at times and this results in an error when the table references the Hold formula

'Error Converting varchar to numeric'

How do I add IS NULL or EMPTY to the above formula, the ISNULL does not catch AvgProfit = ” ??

Answer 1

Consider typing your database with decimal or numeric columns as paxdiablo has suggested. Is there a reason why those columns are set as varchar?

Alternatively if you have to keep your varchar columns, try ISNUMERIC(), http://msdn.microsoft.com/en-us/library/ms186272.aspx. It works with all common SQL numeric types. So you query might become:

ISNUMERIC can be used like this:

select case when ISNUMERIC('123') = 1 then 1 else 0 end ' returns 1
select case when ISNUMERIC('xyz') = 1 then 1 else 0 end ' returns 0
select case when ISNUMERIC(null) = 1 then 1 else 0 end ' returns 0

So your query might become:

case when isnumeric(AvgProfit) = 1 THEN case([AvgProfit] as decimal) else 0 END

Or something similar.