code: func NewPlanBuilder(sctx sessionctx.Context, is infoschema.InfoSchema) *PlanBuilder {
  	return &PlanBuilder{
  		ctx:       sctx,
  		is:        is,
  		colMapper: make(map[*ast.ColumnNameExpr]int),
  	}
  }
docs: // NewPlanBuilder creates a new PlanBuilder.