Sounds rather complicated to me. If it's not too much of a hassle, I would suggest that you redesign your database to use img_id as the primary key (assuming that it is unique). You could then easily calculate the before and after img_id values and select them from the database in 1 SQL query. (It would also be very quick since primary keys are indexed)
my ($img_id) = $str =~ m/img_id=(\d+)/;
my $prev_id = $img_id - 1;
my $next_id = $img_id + 1;

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Then the SQL query (something like):
"select WHATEVER from TABLE where img_id in ($prev_id, $img_id, $next_
+id)"

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Hope this helps,
davidj

In reply to Re: Building an index for next/last in a photo album. by davidj
in thread Building an index for next/last in a photo album. by Seumas

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