Is there any way to do a pattern match against the elements of an array in postgresql (9.4 if the version makes a difference)? I have a grouped query that, among other things, returns an array of values, like:
SELECT lognum, array_agg(flightnum) as flightnums FROM logs GROUP BY lognum;
Where the flightnum field is a varchar containing either a text string or a three-or-four digit number. Now say I want to select all logs that have a flight number starting with an '8' (so '800' or '8000' series flights). My first thought was to do something like this:
SELECT * FROM (SELECT lognum,array_agg(flightnum) as flightnums FROM logs GROUP BY lognum) s1 WHERE '8%' like ANY(flightnums);
But while this doesn't give an error, it also doesn't return any results. I'm guessing that this is because the wildcard is on the left of the operator, and needs to be on the right.
Right. The LIKE operator does not have a commutator by default. (And if you created one for it, it could not use an index in this case.)
Of course, turning it around to be:
WHERE ANY(flightnum) like '8%'
gives me a syntax error. So is there any way I can run this query such that I get any rows containing a flight number that starts with an 8 (or whatever)?
I think you're best bet is to do a subquery against the unaggregated table.
select * from aggregated a where exists
(select 1 from unaggregated ua where a.lognum=ua.lognum and flightnum like '8%')
This is a common problem. If you find a better solution, I'd love to hear it!