derived table and row number addition

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).