implement RowsColumnTypeNullable and RowsColumnTypePrecisionScale interfaces by rows struct to get decimal's precision and scale via func (*Rows) ColumnTypes

https://golang.org/pkg/database/sql/#Rows.ColumnTypes

interfaces are defined here https://github.com/golang/go/blob/master/src/database/sql/driver/driver.go

Author: Sergei Sobolev

lib/column/decimal.go

@@ -239,3 +239,11 @@ func parseDecimal(name, chType string) (Column, error) {
 
 	return decimal, nil
 }
+
+func (d *Decimal) GetPrecision() int {
+	return d.precision
+}
+
+func (d *Decimal) GetScale() int {
+	return d.scale
+}

lib/column/nullable.go

@@ -79,3 +79,7 @@ func parseNullable(name, chType string, timezone *time.Location) (*Nullable, err
 		column: column,
 	}, nil
 }
+
+func (null *Nullable) GetColumn() Column {
+	return null.column
+}

rows.go

@@ -161,3 +161,22 @@ func (rows *rows) setError(err error) error {
 	rows.mutex.Unlock()
 	return err
 }
+
+func (rows *rows) ColumnTypeNullable(idx int) (nullable, ok bool) {
+	_, ok = rows.blockColumns[idx].(*column.Nullable)
+	return ok, true
+}
+
+func (rows *rows) ColumnTypePrecisionScale(idx int) (precision, scale int64, ok bool) {
+	decimalVal, ok := rows.blockColumns[idx].(*column.Decimal)
+	if !ok {
+		if nullable, nullOk := rows.blockColumns[idx].(*column.Nullable); nullOk {
+			decimalVal, ok = nullable.GetColumn().(*column.Decimal)
+		}
+	}
+	if ok {
+		return int64(decimalVal.GetPrecision()), int64(decimalVal.GetScale()), ok
+
+	}
+	return 0, 0, false
+}