diff --git a/migrate/migrate.go b/migrate/migrate.go
index 8f523f92229fd7b9715f44e3ae3a75ac3eec4b39..85c66961649cee596f2b50a7f419ea0bb4e15523 100644
--- a/migrate/migrate.go
+++ b/migrate/migrate.go
@@ -63,6 +63,7 @@ type migrationService struct {
 
 func StartupCheck(logger *zap.Logger, db *sql.DB) {
 	migrate.SetTable(migrationTable)
+	migrate.SetIgnoreUnknown(true)
 
 	ms := &migrate.AssetMigrationSource{
 		Asset: func(path string) ([]byte, error) {
diff --git a/migrate/sql/20210416090601-purchase.sql b/migrate/sql/20210416090601-purchase.sql
index 373baa47a5149e1346a8c873c0459503df567a67..46b4c2450b2a0b4a73f35c770e85cb31f19a920b 100644
--- a/migrate/sql/20210416090601-purchase.sql
+++ b/migrate/sql/20210416090601-purchase.sql
@@ -19,6 +19,7 @@ DROP TABLE IF EXISTS purchase_receipt;
 
 CREATE TABLE IF NOT EXISTS purchase (
     PRIMARY KEY (transaction_id),
+    FOREIGN KEY (user_id) REFERENCES users (id) ON DELETE SET NULL,
 
     create_time    TIMESTAMPTZ  NOT NULL DEFAULT now(),
     environment    SMALLINT     NOT NULL DEFAULT 0, -- Unknown(0), Sandbox(1), Production(2)
@@ -28,7 +29,7 @@ CREATE TABLE IF NOT EXISTS purchase (
     store          SMALLINT     NOT NULL DEFAULT 0, -- AppleAppStore(0), GooglePlay(1), Huawei(2)
     transaction_id VARCHAR(512) NOT NULL CHECK (length(transaction_id) > 0),
     update_time    TIMESTAMPTZ  NOT NULL DEFAULT now(),
-    user_id        UUID         NOT NULL
+    user_id        UUID         DEFAULT NULL
 );
 CREATE INDEX IF NOT EXISTS purchase_user_id_purchase_time_transaction_id_idx
     ON purchase (user_id, purchase_time DESC, transaction_id);
@@ -38,7 +39,6 @@ DROP TABLE IF EXISTS purchase;
 
 CREATE TABLE IF NOT EXISTS purchase_receipt (
     PRIMARY KEY (receipt),
-    FOREIGN KEY (user_id) REFERENCES users (id) ON DELETE NO ACTION,
 
     create_time    TIMESTAMPTZ  NOT NULL DEFAULT now(),
     product_id     VARCHAR(512) NOT NULL,