How to concatenate columns in a Postgres SELECT?

Question

I have two string columns a and b in a table foo.

select a, b from foo returns values a and b<

Answer 1

CONCAT functions sometimes not work with older postgreSQL version

see what I used to solve problem without using CONCAT

 u.first_name || ' ' || u.last_name as user,

Or also you can use

 "first_name" || ' ' || "last_name" as user,

in second case I used double quotes for first_name and last_name

Hope this will be useful, thanks