derived table and row number addition

pgm_field.go

@@ -84,6 +84,43 @@ func (f Field) Desc() Field {
 	return Field(f.String() + " DESC")
 }
 
+func (f Field) RowNumber(as string) Field {
+	return rowNumber(&f, nil, true, as)
+}
+
+func (f Field) RowNumberDesc(as string) Field {
+	return rowNumber(&f, nil, true, as)
+}
+
+// RowNumberPartionBy in ascending order
+func (f Field) RowNumberPartionBy(partition Field, as string) Field {
+	return rowNumber(&f, &partition, true, as)
+}
+
+func (f Field) RowNumberDescPartionBy(partition Field, as string) Field {
+	return rowNumber(&f, &partition, false, as)
+}
+
+func rowNumber(f, partition *Field, isAsc bool, as string) Field {
+	var orderBy string
+	if isAsc {
+		orderBy = " ASC"
+	} else {
+		orderBy = " DESC"
+	}
+
+	if as == "" {
+		as = "row_number"
+	}
+
+	col := f.String()
+	if partition != nil {
+		return Field("ROW_NUMBER() OVER (PARTITION BY " + partition.String() + " ORDER BY " + col + orderBy + ") AS " + as)
+	}
+
+	return Field("ROW_NUMBER() OVER (ORDER BY " + col + orderBy + ") AS " + as)
+}
+
 func (f Field) IsNull() Conditioner {
 	col := f.String()
 	return &Cond{Field: col, op: " IS NULL", len: len(col) + 8}