From: | Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us> |
---|---|
To: | Sam Mason <sam(at)samason(dot)me(dot)uk> |
Cc: | pgsql-general(at)postgresql(dot)org |
Subject: | Re: Functional index adding one |
Date: | 2008-07-03 15:11:26 |
Message-ID: | 2693.1215097886@sss.pgh.pa.us |
Views: | Raw Message | Whole Thread | Download mbox | Resend email |
Thread: | |
Lists: | pgsql-general |
Sam Mason <sam(at)samason(dot)me(dot)uk> writes:
> You just want an extra set of brackets; i.e.:
> CREATE INDEX token_position_func ON token ((position+1));
> Should do the trick. Not entirely sure why, but it'll probably have
> something to do with avoiding ambiguity in the grammar.
Right. The problem is the Berkeley-era decision to put index opclasses
into the syntax without any keyword or punctuation, viz
create index ... on table (column_name [ opclass_name ]);
So something like
CREATE INDEX token_position_func ON token (a + b);
is ambiguous: is the + an infix operator, or is it a postfix operator
and the "b" is to be taken as an opclass name?
We hacked around that by requiring parens around expressions. For
backwards compatibility with other Berkeley-era syntax, there's
a special exception that you can omit the parens when the expression is
just a function call.
regards, tom lane
From | Date | Subject | |
---|---|---|---|
Next Message | Csaba Nagy | 2008-07-03 15:22:47 | Re: Switching between terminals |
Previous Message | Gregory Stark | 2008-07-03 15:09:23 | Re: Switching between terminals |