On Thu, Aug 20, 2015 at 8:19 PM, David G. Johnston <david.g.johnston@xxxxxxxxx> wrote:SELECT [...]FROM (SELECT reference_id, [...] FROM table_where_referenced_id_is_a_pk WHERE reference_id EXISTS/IN/JOIN)srcLEFT JOIN type1 USING (reference_id)LEFT JOIN type2 USING (reference_id)[...]
Place ^ in a CTE named (find_all)
there are no tables where reference_id is a pk, I could create one or do : select reference_id from ( values (..), (...), (...) .... )the tricky part with the join (and where I was not clear about it in my original description) is that a reference_id can match in multiple tables (eg. it can be a fk in type1 and type2), so it then becomes a bit harder to collect all the common attributes and 'types' when doing joins like this.For example let's assume there is a group_id to be be retrieved among all tables as a common attribute:if reference_id was existing only in one table, I could do coalesce(type1.group_id, ... type5.group_id) as group_id in the main selecthowever that would not work in this case.
WITH find_all (reference_id, type_identifier, type_id) AS ( ... )
SELECT type_identifier, array_agg(reference_id), array_agg(type_id)
FROM find_all
WHERE type_identifier IS NOT NULL
GROUP BY type_identifier
find_all will return at least one row, possibly empty if no matches are present, and will return multiple rows if more than one matches. You can use array_agg as shown, or play around with custom composite types, or even build a JSON document.
David J.
