def case_clause(var: nil, statements:, default: nil)
  c_result    = " CASE %{var_input}\n" % {var_input: var}
  c_when_then = " WHEN %{when_input} THEN %{then_input} "
  c_else      = " ELSE %{else_input} END\n"
  c_default   = " DEFAULT %{default} END\n"
  c_end       = " END\n"

  statements.each do |condition, t, f|
    c_result << (c_when_then % {when_input: condition, then_input: t}) << (f.present? ? (c_else % {else_input: f}) : c_end)
  end

  c_result << c_default if default.present?
  c_result << c_end
end