While string interpolation will work, as your question specifies rails 4, you could be using Arel for this and keeping your app database agnostic.
def self.search(query, page=1)
query = "%#{query}%"
name_match = arel_table[:name].matches(query)
postal_match = arel_table[:postal_code].matches(query)
where(name_match.or(postal_match)).page(page).per_page(5)
end