code: func BuildColumnRange(conds []expression.Expression, sc *stmtctx.StatementContext, tp *types.FieldType, colLen int) ([]*Range, error) {
  	if len(conds) == 0 {
  		return []*Range{{LowVal: []types.Datum{{}}, HighVal: []types.Datum{types.MaxValueDatum()}}}, nil
  	}
  	return buildColumnRange(conds, sc, tp, false, colLen)
  }
docs: // BuildColumnRange builds range from access conditions for general columns.