default parameter empty string

[kakom]

I have a stored procedure like this:

create procedure "dba"."xxx"( in @param1 integer,in @param2 integer,in @param3 varchar(4096) default '' ) 
begin
  if @param3 = '' then
/* ... */
  else
/* ... */
  end if
end

Since a long time this worked well as expected. Actually a customer reported a problem and I noticed by testing the following call:

call dba.xxx(11,1)

@param3 comes with value '0'. I am really suprised. Under which circumstances is the default value not reliable?

[kakom]

SQL Anywhere version is 17.0.11.7458

[kakom]

Additional Info: After the @param3 was specified once: call dba.xxx(11,1,'what the hell?') in the next call call dba.xxx(11,1) @param3 came with the last specified value 'what the hell?'

[johnsmirnios]

Did you or your customer connect via TDS? If so, I believe '' is considered equivalent to NULL and comparing anything against NULL would be false (actually 'unknown')?

[kakom]

Thanks John, but this is not the issue. The default parameter did never take the value NULL