Обсуждение: RE: [HACKERS] Associative Operators? (Was: Re: [NOVICE] Out of f rying pan, into fire)

I have not been able to track down any information on coalesce nor get
PostgreSQL execute it.  Where is this documented?
-----Original Message-----From:    Zeugswetter Andreas IZ5
[SMTP:Andreas.Zeugswetter@telecom.at]Sent:    Wednesday, March 17, 1999 1:29 AMTo:    hackers@postgreSQL.orgSubject:
Re:[HACKERS] Associative Operators?  (Was: Re:
 
[NOVICE] Out of f rying  pan, into fire)
>  > >> I tried to create a C function to overcome this but noticed
that if any> >> parameter in my C function is NULL then the C function always
returns> NULL.> >> I saw some references in the archives about this issue but was
unable> to> >> determine where it was left.  What is the status of this issue?> Yes, this is current behavior.
    > Would a compromise be to add DECODE and NVL ?
The Standard has the more flexible function COALESCE, which is
alreadyimplemented in postgresql.Simply say
coalesce(field_that_can_be_null,value_to_return_insteadof_null)
Andreas 

> I have not been able to track down any information on coalesce nor get
> PostgreSQL execute it.  Where is this documented?

Hmm. I seem to not have put it into the docs yet. Look at any SQL book
written in the last few years for details on its usage, or ask here.

btw, COALESCE() is a special case of CASE, which is also implemented,
but which currently has problems with handling results from multiple
tables.
                    - Tom