code: func (nr *nameResolver) handleJoin(j *ast.Join) {
  	if j.Right == nil {
  		j.SetResultFields(j.Left.GetResultFields())
  		return
  	}
  	leftLen := len(j.Left.GetResultFields())
  	rightLen := len(j.Right.GetResultFields())
  	rfs := make([]*ast.ResultField, leftLen+rightLen)
  	copy(rfs, j.Left.GetResultFields())
  	copy(rfs[leftLen:], j.Right.GetResultFields())
  	j.SetResultFields(rfs)
  }
docs: // handleJoin sets result fields for join.