code: def emit_code_from_ir(compound_match_query, compiler_metadata):
      
      # If the compound match query contains only one match query,
      # just call `emit_code_from_single_match_query`
      # If there are multiple match queries, construct the query string for each
      # individual query and combine them as follows.
      #
      # SELECT EXPAND($result)
      # LET
      #    $optional__0 = (
      #        <query_string_0>
      #    ),
      #    $optional__1 = (
      #        <query_string_1>
      #    ),
      #    $optional__2 = (
      #        <query_string_2>
      #    ),
      #
      #    . . .
      #
      #    $result = UNIONALL($optional__0, $optional__1, . . . )
  
      match_queries = compound_match_query.match_queries
      if len(match_queries) == 1:
          query_string = emit_code_from_single_match_query(match_queries[0])
      elif len(match_queries) > 1:
          query_string = emit_code_from_multiple_match_queries(match_queries)
      else:
          raise AssertionError(u'Received CompoundMatchQuery with an empty list of MatchQueries: '
                               u'{}'.format(match_queries))
  
      return query_string
docs: Return a MATCH query string from a CompoundMatchQuery.