Re: TODO list request: FK to unique expression indexes

David E. Wheeler wrote:
> On Nov 19, 2008, at 9:12 AM, Josh Berkus wrote:
> 
> > Folks,
> >
> > Since it's too late to look at this for 8.4, can the following go on  
> > the TODO list?
> >
> > Referential Integrity
> >
> > [] Allow creation of FKs targeting unique expression indexes on the  
> > referenced table.  Syntax: REFERENCES <reftable> ( ( column  
> > expression ) )
> >
> > Reason: current FK rules do not allow creating FKs to columns which  
> > are defined as, for example, unique(lower(column)).  This forces  
> > users to either abandon RI for that table, to store duplicate data,  
> > or create superfluous indexes.
> >
> > Hmmm ... I suppose the above would require enabling expression  
> > indexes for PKs as well, no?
> 
> In 8.4 you should be able to get around this particular example using  
> citext.

Yes, good idea on citext.  

Allowing foreign keys to point to expression indexes seems to open a can
of worms and I am not sure there is enough demand to warrant it.

--  Bruce Momjian  <bruce@momjian.us>        http://momjian.us EnterpriseDB
http://enterprisedb.com
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