derived table and row number addition

Makefile

@@ -1,3 +1,5 @@
+.PHONY: run bench-select test
+
 run:
 	go run ./cmd -o ./playground/db ./playground/schema.sql
 bench-select:

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}

pgm_table.go

@@ -2,10 +2,11 @@ package pgm
 
 // Table in database
 type Table struct {
-	Name       string
-	PK         []string
-	FieldCount uint16
-	debug      bool
+	Name         string
+	DerivedTable Query
+	PK           []string
+	FieldCount   uint16
+	debug        bool
 }
 
 // Debug when set true will print generated query string in stdout
@@ -14,6 +15,10 @@ func (t *Table) Debug() Clause {
 	return t
 }
 
+func (t *Table) Field(f string) Field {
+	return Field(t.Name + "." + f)
+}
+
 // Insert table statement
 func (t *Table) Insert() InsertClause {
 	qb := &insertQry{
@@ -30,10 +35,17 @@ func (t *Table) Insert() InsertClause {
 func (t *Table) Select(field ...Field) SelectClause {
 	qb := &selectQry{
 		debug:  t.debug,
-		table:  t.Name,
 		fields: field,
 	}
 
+	if t.DerivedTable != nil {
+		tName, args := t.DerivedTable.Build(true)
+		qb.table = "(" + tName + ") AS " + t.Name
+		qb.args = args
+	} else {
+		qb.table = t.Name
+	}
+
 	return qb
 }
 

playground/db/derived.go

@@ -0,0 +1,11 @@
+package db
+
+import "code.patial.tech/go/pgm"
+
+func DerivedTable(tblName string, fromQry pgm.Query) pgm.Table {
+	t := pgm.Table{
+		Name:         tblName,
+		DerivedTable: fromQry,
+	}
+	return t
+}

playground/qry_select_test.go

@@ -60,6 +60,27 @@ func TestSelectWithHaving(t *testing.T) {
 	}
 }
 
+func TestSelectDerived(t *testing.T) {
+	expected := "SELECT t.* FROM (SELECT users.*, ROW_NUMBER() OVER (PARTITION BY users.status_id ORDER BY users.created_at DESC) AS rn" +
+		" FROM users WHERE users.status_id = $1) AS t WHERE t.rn <= $2" +
+		" ORDER BY t.status_id, t.created_at DESC"
+
+	qry := db.User.
+		Select(user.All, user.CreatedAt.RowNumberDescPartionBy(user.StatusID, "rn")).
+		Where(user.StatusID.Eq(1))
+
+	tbl := db.DerivedTable("t", qry)
+	got := tbl.
+		Select(tbl.Field("*")).
+		Where(tbl.Field("rn").Lte(5)).
+		OrderBy(tbl.Field("status_id"), tbl.Field("created_at").Desc()).
+		String()
+
+	if expected != got {
+		t.Errorf("\nexpected: %q\n\ngot:      %q", expected, got)
+	}
+}
+
 func TestSelectWithJoin(t *testing.T) {
 	got := db.User.Select(user.Email, user.FirstName).
 		Join(db.UserSession, user.ID, usersession.UserID).

qry_select.go

@@ -7,6 +7,7 @@ import (
 	"context"
 	"errors"
 	"fmt"
+	"slices"
 	"strconv"
 	"strings"
 
@@ -103,6 +104,7 @@ type (
 		First
 		All
 		Stringer
+		Bulder
 	}
 
 	RowScanner interface {
@@ -128,6 +130,10 @@ type (
 		AllTx(ctx context.Context, tx pgx.Tx, rows RowsCb) error
 	}
 
+	Bulder interface {
+		Build(needArgs bool) (qry string, args []any)
+	}
+
 	selectQry struct {
 		table   string
 		fields  []Field
@@ -291,6 +297,17 @@ func (q *selectQry) raw(prefixArgs []any) (string, []any) {
 }
 
 func (q *selectQry) String() string {
+	qry, _ := q.Build(false)
+	if q.debug {
+		fmt.Println("***")
+		fmt.Println(qry)
+		fmt.Printf("%+v\n", q.args)
+		fmt.Println("***")
+	}
+	return qry
+}
+
+func (q *selectQry) Build(needArgs bool) (qry string, args []any) {
 	sb := getSB()
 	defer putSB(sb)
 
@@ -356,14 +373,19 @@ func (q *selectQry) String() string {
 		sb.WriteString(strconv.Itoa(q.offset))
 	}
 
-	qry := sb.String()
+	qry = sb.String()
 	if q.debug {
 		fmt.Println("***")
 		fmt.Println(qry)
 		fmt.Printf("%+v\n", q.args)
 		fmt.Println("***")
 	}
-	return qry
+
+	if needArgs {
+		args = slices.Clone(q.args)
+	}
+
+	return
 }
 
 func (q *selectQry) averageLen() int {