Hi,
I have a question regarding a change in the way GROUP BY has work
between PostgreSQL versions 6.1 and 6.5.2. The latter version's man
page for SELECT says,
"When GROUP BY is present, it is not valid to refer to ungrouped columns except within aggregate functions, since
therewould be more than one possible value to return for an ungrouped column."
This seems sensible. However, version 6.1 did not have this
restriction; for any ungrouped function not within an aggregate, the
first matching value was returned. In effect, a default aggregate was
applied. Unfortunately, my application took advantage of this
behavior. My basic question is, what's the easiest way to duplicate
this behavior using v6.5.2?
Here's a simplified run down of what I am doing, starting with the
tables I'm operating on:
create table projects ( yr int, nimg int, authors text[] ); create table docs ( yr int, im int, title text
);select p.yr,p.nimg,p.authors,d.im,d.title into table joint from projects p,docs d where p.yr=d.yr;
Here's the sort of search I would using the older PG version:
select yr,nimg,authors from joint where title~'word' group by yr;
There is a one-to-many mapping between projects and documents. Thus,
the attributes from the projects table will be duplicated in joint for
each matching record from docs. What I want from the above select are
the projects that contain any doc with a title matching 'word'; but, I
only want one record per project.
The simple solution should be including the other project attributes
list in the select clause in my group-by clause:
select yr,nimg,authors from joint where title~'word' group by yr,nimg,authors;
The problem is that authors is a text array. When I do this, I get the
error message:
ERROR: Unable to identify a binary operator '<' for types _text and
_text
I've also tried creating an aggregate function for text arrays that just
returns the last value encountered; however, the array nature gave me
trouble. (I'll save the details for another posting if necessary.)
many thanks,
Ray Plante