[GENERAL] Slow query when the select list is big

[Sterpu Victor]

I have a big query that takes about 7 seconds to run(time sending the 
data to the client is not counted).
Postgres uses 100% of 1 CPU when solving this query. I tried to run the 
query on a HDD and on a SSD with no difference. HDD show about 10% usage 
while the query runs.

The query has a big "select" list and no "group by" clause. If I delete 
all selects except one the query runs in under a second(it doesn't 
matter what field remains selected).
It seems that the query is slow because of the long select, can I do 
something to make the query faster?

Thank you.