DBNull.Value(数据库写入NULL)与null
DBNull.Value,, 适用于向数据库的表中插入空值。null,是指在程序中表示空引用。 或者对象为空。就是没有实例化。如果要向数据库写NULL，应该写入的是DBNull.Value，而不是直接赋值null。...
Can't place multiple pins assigned to pin location Pin_101
错误：Error (176310): Can't place multiple pins assigned to pin location Pin_101 (IOPAD_X34_Y18_N21) Info (176311): Pin addr[8] is ass...
Warning: xx pins must meet Altera requirements for 3.3-, 3.0-, and 2.5-V interfaces. For more information, refer to AN 447: Interfacing Cyclone IV E Devices with 3.3/3.0/2.5-V LVTTL/LVCMOS I/O Systems
问题描述：Cyclone IV EP4CE6E22C8NQuartus II编译......
c# textbox的passwordchar清空
//三种都是清空this.textBox1.PasswordChar = new char();......
如何统计SQL语句查询出来的条数
可以通过count函数来实现。sqlOne：select * from tablename1 where id>5;此语句查询出来多条记录，之后看做一个新的表。......