diff --git a/internal/data/business/mysql_rehearsal_test.go b/internal/data/business/mysql_rehearsal_test.go
index aeae5ef..de9ea9f 100644
--- a/internal/data/business/mysql_rehearsal_test.go
+++ b/internal/data/business/mysql_rehearsal_test.go
@@ -221,6 +221,47 @@ func TestMySQLRegistrationIndexPreservesCastAndUsesRange(t *testing.T) {
 	}
 }
 
+func TestMySQLLaterRegistrationIndexesPreserveMalformedLegacyTimes(t *testing.T) {
+	db := openRehearsalMySQL(t)
+	for _, sql := range []string{
+		"CREATE TABLE tab_user(id INT,source_db VARCHAR(10),puid INT,promote_id INT,register_time VARCHAR(20),PRIMARY KEY(id,source_db))",
+		"INSERT INTO tab_user VALUES(1,'lx',0,10,''),(2,'lx',0,10,'bad'),(3,'lx',0,10,'1793635200 ')",
+	} {
+		if err := db.Exec(sql).Error; err != nil {
+			t.Fatal(err)
+		}
+	}
+	pool, _ := db.DB()
+	pool.SetMaxOpenConns(1)
+	var mode string
+	if err := db.Raw("SELECT @@session.sql_mode").Scan(&mode).Error; err != nil {
+		t.Fatal(err)
+	}
+	if err := migrateRegistrationIndex(db); err != nil {
+		t.Fatal(err)
+	}
+	indexes := []businessQueryIndex{{"tab_user", "idx_alert_user_window", []string{"source_db", "promote_id", "sw_register_time_unix", "puid"}}}
+	for i := 0; i < 2; i++ {
+		if err := migrateQueryIndexes(db, indexes); err != nil {
+			t.Fatal(err)
+		}
+	}
+	var after string
+	if err := db.Raw("SELECT @@session.sql_mode").Scan(&after).Error; err != nil || mode != after {
+		t.Fatalf("sql_mode changed: %v", err)
+	}
+	var values []string
+	if err := db.Table("tab_user").Order("id").Pluck("register_time", &values).Error; err != nil || strings.Join(values, "|") != "|bad|1793635200 " {
+		t.Fatalf("original strings changed: %q %v", values, err)
+	}
+	if err := migrateQueryIndexes(db, []businessQueryIndex{{"tab_user", "idx_invalid_column", []string{"missing_column"}}}); err == nil {
+		t.Fatal("invalid DDL unexpectedly succeeded")
+	}
+	if err := db.Raw("SELECT @@session.sql_mode").Scan(&after).Error; err != nil || mode != after {
+		t.Fatalf("failed DDL did not restore sql_mode: %v", err)
+	}
+}
+
 func TestMySQLChannelCreationSerializesAccount(t *testing.T) {
 	db := openRehearsalMySQL(t)
 	if err := db.AutoMigrate(&platformChannelPO{}, &channelSettlementPO{}); err != nil {
diff --git a/internal/data/business/query_indexes.go b/internal/data/business/query_indexes.go
index 36d22fa..2b63528 100644
--- a/internal/data/business/query_indexes.go
+++ b/internal/data/business/query_indexes.go
@@ -74,7 +74,17 @@ func migrateQueryIndexes(db *gorm.DB, indexes []businessQueryIndex) error {
 		}
 		// 同一大表的多个索引合并构建，减少重复扫描。
 		if len(additions) > 0 {
-			if err := db.Exec("ALTER TABLE `" + table + "` " + strings.Join(additions, ",") + ", ALGORITHM=INPLACE, LOCK=NONE").Error; err != nil {
+			build := func(conn *gorm.DB) error {
+				return conn.Exec("ALTER TABLE `" + table + "` " + strings.Join(additions, ",") + ", ALGORITHM=INPLACE, LOCK=NONE").Error
+			}
+			// Later indexes also evaluate the historical generated time column.
+			// Apply the same connection-local compatibility rule as its first index.
+			if table == "tab_user" && db.Migrator().HasColumn(table, "sw_register_time_unix") {
+				err = withLegacyRegistrationCast(db, build)
+			} else {
+				err = build(db)
+			}
+			if err != nil {
 				return fmt.Errorf("add query indexes on %s: %w", table, err)
 			}
 		}
diff --git a/internal/data/business/registration_index.go b/internal/data/business/registration_index.go
index eb10733..3e5d633 100644
--- a/internal/data/business/registration_index.go
+++ b/internal/data/business/registration_index.go
@@ -44,11 +44,20 @@ func migrateRegistrationIndex(db *gorm.DB) error {
 }
 
 func addRegistrationIndex(db *gorm.DB) error {
+	return withLegacyRegistrationCast(db, func(conn *gorm.DB) error {
+		return conn.Exec("ALTER TABLE tab_user ADD INDEX idx_sw_user_registration(source_db,puid,sw_register_time_unix,id), ALGORITHM=INPLACE, LOCK=NONE").Error
+	})
+}
+
+func withLegacyRegistrationCast(db *gorm.DB, migrate func(*gorm.DB) error) error {
 	// 旧 SELECT CAST 会以警告方式接受尾部空格等历史值。建索引属于 DDL，
 	// 严格模式会把同一警告升级为错误；仅在固定连接的索引构建期间保持旧转换行为。
 	return db.Connection(func(conn *gorm.DB) (result error) {
+		// Keep the bound connection's base handle free of statement errors so
+		// restoration still executes after a failed ALTER TABLE.
+		fresh := func() *gorm.DB { return conn.Session(&gorm.Session{NewDB: true}) }
 		var previous string
-		if err := conn.Raw("SELECT @@session.sql_mode").Scan(&previous).Error; err != nil {
+		if err := fresh().Raw("SELECT @@session.sql_mode").Scan(&previous).Error; err != nil {
 			return err
 		}
 		modes := []string{}
@@ -57,14 +66,14 @@ func addRegistrationIndex(db *gorm.DB) error {
 				modes = append(modes, mode)
 			}
 		}
-		if err := conn.Exec("SET SESSION sql_mode=?", strings.Join(modes, ",")).Error; err != nil {
+		if err := fresh().Exec("SET SESSION sql_mode=?", strings.Join(modes, ",")).Error; err != nil {
 			return err
 		}
 		defer func() {
-			if err := conn.Exec("SET SESSION sql_mode=?", previous).Error; err != nil {
+			if err := fresh().Exec("SET SESSION sql_mode=?", previous).Error; err != nil {
 				result = errors.Join(result, err)
 			}
 		}()
-		return conn.Exec("ALTER TABLE tab_user ADD INDEX idx_sw_user_registration(source_db,puid,sw_register_time_unix,id), ALGORITHM=INPLACE, LOCK=NONE").Error
+		return migrate(fresh())
 	})
 }