Question

I have a table that has a column ‘Value’ that is a varchar. One row puts a ’10’ in this column. This “number” will need to be added and substracted to, but I can do so directly b/c its a varchar.
So, the following gives an error:

update Fields  
set Value = Value - 1
from Fields f, FTypes ft
where ft.Name = 'Field Count'
    and ft.ID = f.ID_FT
    and f.ID_Project = 186              

GO

How do I cast/convert the value to an int, perform the math, then set as a varchar again?

Answer 1

Martin Smith’s point is an excellent one –> If it is only numeric data going in there and you are always going to be doing operations like this, it will save you time and hassle not having to do this conversion work.

That being said you can do –

update Fields  
set ColumnName = cast( (cast(ColumnName as int) - 1) as varchar(nn))
from Fields f, FTypes ft
where ft.Name = 'Field Count'
    and ft.ID = f.ID_FT
    and f.ID_Project = 186   

where nn is the original definition of your varchar column