According to the docs:
First, I don't understand this. Second, the linked java docs don't mention comma anywhere. Is it possible to have commas in the number output?
Looks like maybe #,## will do it? Testing.
I assume that you mean using comma as the decimal separator? If so, this is by default controlled by the locale. In the Decimal Format pattern, a period always represents the decimal separator but it is replaced with the current locale's separator character when formatting a number. For instance, with a Swedish locale a comma is used as the decimal separator, while a period is used for an English locale.
If you are using DbVisualizer 9.5.3 or later, you can override the locale defaults by setting the Decimal (and Grouping) separator separately.