local list = MySQL.Sync.fetchAll('SELECT * FROM `empresas`')
print(list[1].empresa_nome) -- This gives you the first result of you query.
I would recommend checking for a name like this:
local nameToCheck = "aa"
local list = MySQL.Sync.fetchAll('SELECT * FROM `empresas` WHERE empresa_nome = ?', {nameToCheck})
if list[1] then
-- The name exist.
else
-- The name dosent exist.
end