db.Exec("UPDATE consultations SET serial_number = 'C00000000-' || LPAD(CAST(ROW_NUMBER() OVER (ORDER BY created_at) AS TEXT), 4, '0') WHERE serial_number IS NULL OR serial_number = ''")
}else{
// 列不存在时先添加为可空,填值后再由 AutoMigrate 加约束
db.Exec("ALTER TABLE consultations ADD COLUMN IF NOT EXISTS serial_number VARCHAR(20)")
db.Exec("UPDATE consultations SET serial_number = 'C00000000-' || LPAD(CAST(ROW_NUMBER() OVER (ORDER BY created_at) AS TEXT), 4, '0') WHERE serial_number IS NULL OR serial_number = ''")