diff --git a/src/query.zig b/src/query.zig
index 06581b5..b39858f 100644
--- a/src/query.zig
+++ b/src/query.zig
@@ -2065,3 +2065,162 @@ test "selectPageOrdered with an empty order-by falls through to selectPage's ear
     for (ordered, plain) |o, p| try std.testing.expectEqual(o.get(pkField).?.int, p.get(pkField).?.int);
 }
 
+test "createCompositeIndex backfills then full-tuple eq select uses it" {
+    const allocator = std.testing.allocator;
+    var tmp = std.testing.tmpDir(.{});
+    defer tmp.cleanup();
+    var db = try openTemp(&tmp, allocator);
+    defer db.close();
+
+    var table = try Table.open(&db, allocator, "users");
+    defer table.deinit();
+
+    try table.put(.{ .int = 1 }, &.{
+        .{ .name = "city", .value = .{ .text = "warsaw" } },
+        .{ .name = "age", .value = .{ .int = 30 } },
+    });
+    try table.put(.{ .int = 2 }, &.{
+        .{ .name = "city", .value = .{ .text = "warsaw" } },
+        .{ .name = "age", .value = .{ .int = 40 } },
+    });
+    try table.put(.{ .int = 3 }, &.{
+        .{ .name = "city", .value = .{ .text = "krakow" } },
+        .{ .name = "age", .value = .{ .int = 30 } },
+    });
+
+    try table.createCompositeIndex("city_age", &.{ "city", "age" });
+    try std.testing.expect(table.hasCompositeIndex("city_age"));
+
+    const preds = [_]Predicate{
+        .{ .eq = .{ .field = "city", .value = .{ .text = "warsaw" } } },
+        .{ .eq = .{ .field = "age", .value = .{ .int = 30 } } },
+    };
+    const results = try table.select(.{ .and_ = &preds });
+    defer freeRows(allocator, results);
+    try std.testing.expectEqual(@as(usize, 1), results.len);
+    try std.testing.expectEqual(@as(i64, 1), results[0].get(pkField).?.int);
+}
+
+test "composite index leftmost prefix narrows without constraining every column" {
+    const allocator = std.testing.allocator;
+    var tmp = std.testing.tmpDir(.{});
+    defer tmp.cleanup();
+    var db = try openTemp(&tmp, allocator);
+    defer db.close();
+
+    var table = try Table.open(&db, allocator, "users");
+    defer table.deinit();
+    try table.createCompositeIndex("city_age", &.{ "city", "age" });
+
+    try table.put(.{ .int = 1 }, &.{
+        .{ .name = "city", .value = .{ .text = "warsaw" } },
+        .{ .name = "age", .value = .{ .int = 30 } },
+    });
+    try table.put(.{ .int = 2 }, &.{
+        .{ .name = "city", .value = .{ .text = "warsaw" } },
+        .{ .name = "age", .value = .{ .int = 40 } },
+    });
+    try table.put(.{ .int = 3 }, &.{
+        .{ .name = "city", .value = .{ .text = "krakow" } },
+        .{ .name = "age", .value = .{ .int = 50 } },
+    });
+
+    // Only the leading column is constrained - the composite index must
+    // still narrow the scan to the two warsaw rows via its leftmost prefix,
+    // and the (unindexed-alone) age column is unconstrained here.
+    const results = try table.select(.{ .eq = .{ .field = "city", .value = .{ .text = "warsaw" } } });
+    defer freeRows(allocator, results);
+    try std.testing.expectEqual(@as(usize, 2), results.len);
+}
+
+test "composite index uses a range bound on the column after the matched prefix" {
+    const allocator = std.testing.allocator;
+    var tmp = std.testing.tmpDir(.{});
+    defer tmp.cleanup();
+    var db = try openTemp(&tmp, allocator);
+    defer db.close();
+
+    var table = try Table.open(&db, allocator, "users");
+    defer table.deinit();
+    try table.createCompositeIndex("city_age", &.{ "city", "age" });
+
+    var age: i64 = 20;
+    while (age < 30) : (age += 1) {
+        try table.put(.{ .int = age }, &.{
+            .{ .name = "city", .value = .{ .text = "warsaw" } },
+            .{ .name = "age", .value = .{ .int = age } },
+        });
+        try table.put(.{ .int = age + 100 }, &.{
+            .{ .name = "city", .value = .{ .text = "krakow" } },
+            .{ .name = "age", .value = .{ .int = age } },
+        });
+    }
+
+    // city == "warsaw" and 23 <= age < 27: must stay inside the warsaw
+    // bucket of the composite index even though krakow rows overlap the
+    // same age range byte-for-byte.
+    const preds = [_]Predicate{
+        .{ .eq = .{ .field = "city", .value = .{ .text = "warsaw" } } },
+        .{ .gte = .{ .field = "age", .value = .{ .int = 23 } } },
+        .{ .lt = .{ .field = "age", .value = .{ .int = 27 } } },
+    };
+    const results = try table.select(.{ .and_ = &preds });
+    defer freeRows(allocator, results);
+    try std.testing.expectEqual(@as(usize, 4), results.len);
+    for (results) |r| {
+        try std.testing.expectEqualStrings("warsaw", r.get("city").?.text);
+        try std.testing.expect(r.get("age").?.int >= 23 and r.get("age").?.int < 27);
+    }
+
+    // A one-sided range (age > 27) narrows the same way.
+    const openPreds = [_]Predicate{
+        .{ .eq = .{ .field = "city", .value = .{ .text = "warsaw" } } },
+        .{ .gt = .{ .field = "age", .value = .{ .int = 27 } } },
+    };
+    const openResults = try table.select(.{ .and_ = &openPreds });
+    defer freeRows(allocator, openResults);
+    try std.testing.expectEqual(@as(usize, 2), openResults.len);
+    for (openResults) |r| {
+        try std.testing.expectEqualStrings("warsaw", r.get("city").?.text);
+        try std.testing.expect(r.get("age").?.int > 27);
+    }
+}
+
+test "composite index stays in sync across update and delete" {
+    const allocator = std.testing.allocator;
+    var tmp = std.testing.tmpDir(.{});
+    defer tmp.cleanup();
+    var db = try openTemp(&tmp, allocator);
+    defer db.close();
+
+    var table = try Table.open(&db, allocator, "users");
+    defer table.deinit();
+    try table.createCompositeIndex("city_age", &.{ "city", "age" });
+
+    const preds = [_]Predicate{
+        .{ .eq = .{ .field = "city", .value = .{ .text = "warsaw" } } },
+        .{ .eq = .{ .field = "age", .value = .{ .int = 30 } } },
+    };
+    const pred = Predicate{ .and_ = &preds };
+
+    try table.put(.{ .int = 1 }, &.{
+        .{ .name = "city", .value = .{ .text = "warsaw" } },
+        .{ .name = "age", .value = .{ .int = 30 } },
+    });
+    {
+        const found = try table.select(pred);
+        defer freeRows(allocator, found);
+        try std.testing.expectEqual(@as(usize, 1), found.len);
+    }
+
+    // Moving age away from 30 must drop the old composite entry.
+    try table.put(.{ .int = 1 }, &.{
+        .{ .name = "city", .value = .{ .text = "warsaw" } },
+        .{ .name = "age", .value = .{ .int = 31 } },
+    });
+    {
+        const stale = try table.select(pred);
+        defer freeRows(allocator, stale);
+        try std.testing.expectEqual(@as(usize, 0), stale.len);
+    }
+