diff --git a/internal/difftest/normalize.go b/internal/difftest/normalize.go
new file mode 100644
index 0000000..c5d2cd6
--- /dev/null
+++ b/internal/difftest/normalize.go
@@ -0,0 +1,91 @@
+package difftest
+
+import (
+	"fmt"
+	"sort"
+	"strings"
+
+	"github.com/aybavs/sql-query-engine/internal/value"
+)
+
+// nullCell is a sentinel no literal in the generated grammar can produce, so a
+// text value never masquerades as NULL.
+const nullCell = "∅"
+
+// normalizeEngineRow renders one engine row as comparable cells. Cells carry a
+// type tag so the text "35" cannot compare equal to the number 35.
+func normalizeEngineRow(r value.Row) []string {
+	out := make([]string, len(r))
+	for i, v := range r {
+		switch {
+		case v.IsNull():
+			out[i] = nullCell
+		case v.Type == value.TInt:
+			out[i] = num(float64(v.I))
+		case v.Type == value.TFloat:
+			out[i] = num(v.F)
+		case v.Type == value.TBool:
+			out[i] = fmt.Sprintf("b:%t", v.B)
+		default:
+			out[i] = "s:" + v.S
+		}
+	}
+	return out
+}
+
+// normalizeOracleRow renders one SQLite driver row the same way.
+func normalizeOracleRow(r Row) []string {
+	out := make([]string, len(r))
+	for i, cell := range r {
+		switch v := cell.(type) {
+		case nil:
+			out[i] = nullCell
+		case int64:
+			out[i] = num(float64(v))
+		case float64:
+			out[i] = num(v)
+		case bool:
+			out[i] = fmt.Sprintf("b:%t", v)
+		case []byte:
+			out[i] = "s:" + string(v)
+		case string:
+			out[i] = "s:" + v
+		default:
+			out[i] = fmt.Sprintf("?:%v", v)
+		}
+	}
+	return out
+}
+
+// num renders a number so an integer and an equal float compare the same.
+// SQLite returns an average as a float where this engine may return an int, and
+// the two can disagree in the last bits; six significant digits absorb that
+// noise while still separating genuinely different values.
+func num(f float64) string { return fmt.Sprintf("n:%.6g", f) }
+
+// canonical sorts rows so two result sets can be compared as multisets. Row
+// order is unspecified in SQL without ORDER BY, so the comparison must not
+// depend on it — but duplicates still have to match.
+func canonical(rows [][]string) []string {
+	out := make([]string, len(rows))
+	for i, r := range rows {
+		out[i] = strings.Join(r, "\x1f")
+	}
+	sort.Strings(out)
+	return out
+}
+
+// Compare reports whether two result sets hold the same rows, ignoring order
+// but respecting duplicates.
+func Compare(engine, oracle [][]string) error {
+	a, b := canonical(engine), canonical(oracle)
+	if len(a) != len(b) {
+		return fmt.Errorf("row count: engine %d, sqlite %d\n  engine: %v\n  sqlite: %v", len(a), len(b), a, b)
+	}
+	for i := range a {
+		if a[i] != b[i] {
+			return fmt.Errorf("row %d differs:\n  engine: %s\n  sqlite: %s", i, a[i], b[i])
+		}
+	}
+	return nil
+}
diff --git a/internal/difftest/normalize_test.go b/internal/difftest/normalize_test.go
new file mode 100644
index 0000000..b60a636
--- /dev/null
+++ b/internal/difftest/normalize_test.go
@@ -0,0 +1,86 @@
+package difftest
+
+import (
+	"testing"
+
+	"github.com/aybavs/sql-query-engine/internal/value"
+)
+
+func TestNormalizeMatchesIntAndFloat(t *testing.T) {
+	eng := normalizeEngineRow(value.Row{value.Int64(35)})
+	orc := normalizeOracleRow(Row{float64(35)})
+	if eng[0] != orc[0] {
+		t.Fatalf("int 35 = %q but float 35.0 = %q; they must normalize alike", eng[0], orc[0])
+	}
+}
+
+func TestNormalizeNull(t *testing.T) {
+	eng := normalizeEngineRow(value.Row{value.NullOf(value.TInt)})
+	orc := normalizeOracleRow(Row{nil})
+	if eng[0] != orc[0] {
+		t.Fatalf("NULL normalized differently: %q vs %q", eng[0], orc[0])
+	}
+}
+
+func TestNormalizeTextIsNotConfusedWithNull(t *testing.T) {
+	eng := normalizeEngineRow(value.Row{value.Text("NULL")})
+	orc := normalizeOracleRow(Row{nil})
+	if eng[0] == orc[0] {
+		t.Fatal("the text 'NULL' must not normalize to the NULL sentinel")
+	}
+}
+
+func TestNormalizeTextIsNotConfusedWithNumber(t *testing.T) {
+	eng := normalizeEngineRow(value.Row{value.Text("35")})
+	orc := normalizeOracleRow(Row{int64(35)})
+	if eng[0] == orc[0] {
+		t.Fatal("the text '35' must not normalize to the number 35")
+	}
+}
+
+func TestNormalizeAbsorbsFloatNoise(t *testing.T) {
+	// An average computed two different ways can differ in the last bits.
+	a := normalizeEngineRow(value.Row{value.Float64(35.0)})
+	b := normalizeOracleRow(Row{35.000000000000004})
+	if a[0] != b[0] {
+		t.Fatalf("float noise must not read as a difference: %q vs %q", a[0], b[0])
+	}
+}
+
+func TestNormalizeKeepsRealNumericDifference(t *testing.T) {
+	a := normalizeEngineRow(value.Row{value.Float64(35.0)})
+	b := normalizeOracleRow(Row{35.1})
+	if a[0] == b[0] {
+		t.Fatal("35.0 and 35.1 are genuinely different and must not normalize alike")
+	}
+}
+
+func TestCompareIgnoresRowOrder(t *testing.T) {
+	a := [][]string{{"1"}, {"2"}}
+	b := [][]string{{"2"}, {"1"}}
+	if err := Compare(a, b); err != nil {
+		t.Fatalf("row order must not matter: %v", err)
+	}
+}
+
+func TestCompareDetectsDifference(t *testing.T) {
+	a := [][]string{{"1"}, {"2"}}
+	b := [][]string{{"1"}, {"3"}}
+	if err := Compare(a, b); err == nil {
+		t.Fatal("differing multisets must be reported")
+	}
+}
+
+func TestCompareDetectsDuplicateCount(t *testing.T) {
+	a := [][]string{{"1"}, {"1"}}
+	b := [][]string{{"1"}}
+	if err := Compare(a, b); err == nil {
+		t.Fatal("duplicate counts must matter")
+	}
+}
+
+func TestCompareEmptyResultsMatch(t *testing.T) {
+	if err := Compare(nil, nil); err != nil {
+		t.Fatalf("two empty result sets must match: %v", err)
+	}
+}