摘要:
报错语句: delete from users where username in ( select username from users where enabled = 0 ) 解决办法: 修改子查询,多嵌套一层 delete from users where username in ( sel 阅读全文
摘要:
饿汉式 public class Singleton{ //类加载时就初始化 private static final Singleton INSTANCE = new Singleton(); //构造方法必须私有 private Singleton(){} //提供获取对象的方法 public 阅读全文