Postgres 12

By using db<>fiddle, you agree to license everything you submit by Creative Commons CC0.

drop table if exists my_table;
create table my_table(id serial primary key, abbrevs text);
insert into my_table (abbrevs) values
('BG MSG');

drop table if exists substitutions;
create table substitutions(target text, replacement text);
insert into substitutions values
('BG',  'Brick Galvan'),
('MSG', 'Mosaic Galvan');

DROP TABLE

CREATE TABLE

INSERT 0 1

DROP TABLE

CREATE TABLE

INSERT 0 2

select id, unnest(string_to_array(abbrevs, ' ')) as abbrev
from my_table

id
abbrev

1
BG

1
MSG

SELECT 2

select id, string_agg(replacement, ' ') as full_names
from (
    select id, unnest(string_to_array(abbrevs, ' ')) as abbrev
    from my_table
    ) t
join substitutions on abbrev = target
group by id

id
full_names

1
Brick Galvan Mosaic Galvan

SELECT 1