Obtaining advisory lock using ORDER BY

Hi all.
 
I have this "dequeue" query which is working:
 
select qe.entity_id, qe.queue_id, qe.sequence_id, qe.tx_id , qe.payload_string
fromorigo_queue_entry qe WHERE qe.queue_id = 2 AND pg_try_advisory_xact_lock(
sequence_id) LIMIT 1 FOR UPDATE ;
I'm not sure is this is guaranteed to lock in ASC-order on column sequence_id,
is it?
 
To ensure this I've tried with an explicit ORDER BY on "sequence_id", like
this:
 
select qe.entity_id, qe.queue_id, qe.sequence_id, qe.tx_id , qe.payload_string
fromorigo_queue_entry qe WHERE qe.queue_id = 2 AND pg_try_advisory_xact_lock(
sequence_id) ORDER BY qe.sequence_id ASC LIMIT 1 FOR UPDATE ;

But the latter query results in all non-locked rows being locked (but it
returns only 1 row due to LIMIT 1), but I'd like the "lowest" non-loced one.
 
Is there a way to make the locking work on an custom ordered set, preserving
the "LIMIT 1"?
 
Thanks.
 
-- Andreas Joseph Krogh
CTO / Partner - Visena AS
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