diff --git a/src/query.zig b/src/query.zig
index a49496f..978cd99 100644
--- a/src/query.zig
+++ b/src/query.zig
@@ -3017,3 +3017,160 @@ test "unique constraint survives a table reopen (persisted across process restar
         try table.put(.{ .int = 1 }, &.{.{ .name = "email", .value = .{ .text = "a@x.com" } }});
     }
 
+    var reopened = try Table.open(&db, allocator, "users");
+    defer reopened.deinit();
+    try std.testing.expect(reopened.hasUniqueIndex("email"));
+    try std.testing.expectError(error.UniqueViolation, reopened.put(.{ .int = 2 }, &.{
+        .{ .name = "email", .value = .{ .text = "a@x.com" } },
+    }));
+}
+
+test "createUniqueIndex rejects a bad field identifier" {
+    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 std.testing.expectError(error.InvalidIdentifier, table.createUniqueIndex("bad\x00field"));
+}
+
+test "rows missing the unique field entirely never collide with each other" {
+    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 = "age", .value = .{ .int = 20 } }});
+    try table.put(.{ .int = 2 }, &.{.{ .name = "age", .value = .{ .int = 21 } }});
+
+    try table.createUniqueIndex("email");
+    try table.put(.{ .int = 3 }, &.{.{ .name = "age", .value = .{ .int = 22 } }});
+    const rows = try table.scanAll();
+    defer freeRows(allocator, rows);
+    try std.testing.expectEqual(@as(usize, 3), rows.len);
+}
+
+test "createForeignKey against the primary key rejects a dangling reference and accepts a real one" {
+    const allocator = std.testing.allocator;
+    var tmp = std.testing.tmpDir(.{});
+    defer tmp.cleanup();
+    var db = try openTemp(&tmp, allocator);
+    defer db.close();
+
+    var customers = try Table.open(&db, allocator, "customers");
+    defer customers.deinit();
+    try customers.put(.{ .int = 1 }, &.{.{ .name = "name", .value = .{ .text = "Ada" } }});
+
+    var orders = try Table.open(&db, allocator, "orders");
+    defer orders.deinit();
+    try orders.createForeignKey("customer_id", "customers", pkField, .restrict);
+    try std.testing.expect(orders.hasForeignKey("customer_id"));
+
+    try orders.put(.{ .int = 100 }, &.{.{ .name = "customer_id", .value = .{ .int = 1 } }});
+
+    try std.testing.expectError(error.ForeignKeyViolation, orders.put(.{ .int = 101 }, &.{
+        .{ .name = "customer_id", .value = .{ .int = 999 } },
+    }));
+}
+
+test "createForeignKey against a UNIQUE non-pk field works, and refuses a target with no unique backing" {
+    const allocator = std.testing.allocator;
+    var tmp = std.testing.tmpDir(.{});
+    defer tmp.cleanup();
+    var db = try openTemp(&tmp, allocator);
+    defer db.close();
+
+    var products = try Table.open(&db, allocator, "products");
+    defer products.deinit();
+    try products.put(.{ .int = 1 }, &.{.{ .name = "sku", .value = .{ .text = "SKU-1" } }});
+
+    var lineItems = try Table.open(&db, allocator, "line_items");
+    defer lineItems.deinit();
+
+    // "sku" has no unique constraint on products yet.
+    try std.testing.expectError(error.ForeignKeyRequiresUniqueTarget, lineItems.createForeignKey("product_sku", "products", "sku", .restrict));
+
+    try products.createUniqueIndex("sku");
+    try lineItems.createForeignKey("product_sku", "products", "sku", .restrict);
+
+    try lineItems.put(.{ .int = 1 }, &.{.{ .name = "product_sku", .value = .{ .text = "SKU-1" } }});
+    try std.testing.expectError(error.ForeignKeyViolation, lineItems.put(.{ .int = 2 }, &.{
+        .{ .name = "product_sku", .value = .{ .text = "NOPE" } },
+    }));
+}
+
+test "createForeignKey refuses to install over a child row that already dangles" {
+    const allocator = std.testing.allocator;
+    var tmp = std.testing.tmpDir(.{});
+    defer tmp.cleanup();
+    var db = try openTemp(&tmp, allocator);
+    defer db.close();
+
+    var customers = try Table.open(&db, allocator, "customers");
+    defer customers.deinit();
+
+    var orders = try Table.open(&db, allocator, "orders");
+    defer orders.deinit();
+    try orders.put(.{ .int = 1 }, &.{.{ .name = "customer_id", .value = .{ .int = 42 } }});
+
+    try std.testing.expectError(error.ForeignKeyViolation, orders.createForeignKey("customer_id", "customers", pkField, .restrict));
+    try std.testing.expect(!orders.hasForeignKey("customer_id"));
+}
+
+test "a row with no value for the foreign key field is exempt from the constraint" {
+    const allocator = std.testing.allocator;
+    var tmp = std.testing.tmpDir(.{});
+    defer tmp.cleanup();
+    var db = try openTemp(&tmp, allocator);
+    defer db.close();
+
+    var customers = try Table.open(&db, allocator, "customers");
+    defer customers.deinit();
+
+    var orders = try Table.open(&db, allocator, "orders");
+    defer orders.deinit();
+    try orders.createForeignKey("customer_id", "customers", pkField, .restrict);
+
+    // No "customer_id" field at all - a nullable foreign key, not a violation.
+    try orders.put(.{ .int = 1 }, &.{.{ .name = "note", .value = .{ .text = "guest checkout" } }});
+    var row = (try orders.get(.{ .int = 1 })).?;
+    defer row.deinit();
+    try std.testing.expect(row.get("customer_id") == null);
+}
+
+test "dropForeignKey lifts the constraint" {
+    const allocator = std.testing.allocator;
+    var tmp = std.testing.tmpDir(.{});
+    defer tmp.cleanup();
+    var db = try openTemp(&tmp, allocator);
+    defer db.close();
+
+    var customers = try Table.open(&db, allocator, "customers");
+    defer customers.deinit();
+
+    var orders = try Table.open(&db, allocator, "orders");
+    defer orders.deinit();
+    try orders.createForeignKey("customer_id", "customers", pkField, .restrict);
+
+    try std.testing.expectError(error.ForeignKeyViolation, orders.put(.{ .int = 1 }, &.{
+        .{ .name = "customer_id", .value = .{ .int = 42 } },
+    }));
+
+    try orders.dropForeignKey("customer_id");
+    try std.testing.expect(!orders.hasForeignKey("customer_id"));
+    try orders.put(.{ .int = 1 }, &.{.{ .name = "customer_id", .value = .{ .int = 42 } }});
+}
+
+test "deleting a parent row is restricted while a child still references it via the primary key" {
+    const allocator = std.testing.allocator;
+    var tmp = std.testing.tmpDir(.{});
+    defer tmp.cleanup();
+    var db = try openTemp(&tmp, allocator);
+    defer db.close();
+