>>I have a "comment" field in a table that I want populated if another field
>>has a certain value. Is it possible to set a check constraint for this?
>>
>>Example:
>>Let's say we have fields
>>Purchase_type smallint check(purchase_type <4)
>>comment varchar
>>
>>I need a check rule to something like (pseudo code)
>>check (if purchase_type = 3 then NOT NULL comment)
>
> No - you'll want a BEFORE UPDATE/INSERT trigger. It shouldn't be difficult to
> do though.
I don't see why not:
CHECK ((purchase_type <> 3) OR ((purchase_type = 3) AND comment IS NOT
NULL))