code: func BuiltinValuesFactory(offset int) BuiltinFunc {
  	return func(_ []types.Datum, ctx context.Context) (d types.Datum, err error) {
  		values := ctx.GetSessionVars().CurrInsertValues
  		if values == nil {
  			err = errors.New("Session current insert values is nil")
  			return
  		}
  		row := values.([]types.Datum)
  		if len(row) > offset {
  			return row[offset], nil
  		}
  		err = errors.Errorf("Session current insert values len %d and column's offset %v don't match", len(row), offset)
  		return
  	}
  }
docs: // BuiltinValuesFactory generates values builtin function.