Question: How can I get "select from_unixtime(max(clock)) from history;" (12 mins required!) as quickly as "select max(itemid) from history;" [quote][font=] mysql> select from_unixtime(max(clock)) from history; +---------------------------+ | from_unixtime(max(clock)) | +---------------------------+ | 2009-03-05 13:52:46 | +---------------------------+ 1 row in set (12 min 12.93 sec) mysql...
java代码如下 String sql="select max(a.fplx) from tfp_zyfplxmx a"; PreparedStatement stmt = conn.prepareStatement(sql); rs = stmt.executeQuery(); while(rs.next()){ ss=rs.getString(1); system.out.println("33333 "+ss); } rs 不是空的 但是 打印信息 显示 33333 null 而且把sql 放在pl/sql里执行 是可以查到数据的 为什么会这样 要怎么解决? 是不是跟ora的缓存有关系?
java代码如下 String sql="select max(a.fplx) from tfp_zyfplxmx a"; PreparedStatement stmt = conn.prepareStatement(sql); rs = stmt.executeQuery(); while(rs.next()){ ss=rs.getString(1); } rs 不是空的 但是 ss=null 而且把sql 放在pl/sql里执行 是可以查到数据的 是不是跟ora的缓存有关系?
如题,如果刚插入一条,可以用mysql_insert_id()得到,有时候在查询中经常需要引用最大ID号,有没有现成的函数或好的方法?
问题挺弱,要取id=001记录的日期最大的记录,有什么方法,除了用字查询select * from tb wher id='001' and date1=(select max(date1) from tb where id='001' ) 。
Quite often when you’re writing Linux applications, you may need to examine the state of a number of inputs to determine the next action to take. For example, a communication program such as a terminal emulator needs to read the keyboard and the serial port effectively at the same time. In a single-user system, it might be acceptable to run in a “busy wait” loop, repeatedly scanning the input f...
void fun() { int i; int ch; struct timeval timeout; timeout.tv_sec=1; timeout.tv_usec=0; fd_set readfds; FD_ZERO(&readfds); FD_SET(0,&readfds); i=select(1,&readfds,NULL,NULL,&timeout); if(i==1) ch=getchar(); printf("%c",ch); fun(); } int main() { pid_t pid; if((pid=vfork())==0)fun(); while(1); return 1; } ------------------------- 我原是想通过fun来监听键...
一、winsock中 #include 原型 int select( int nfds , fd_set* readfds , fd_set* writefds , fd_set* exceptfds , const struct timeval* timeout ); nfds:本参数忽略,仅起到兼容作用。 readfds:(可选)指针,指向一组等待可读性检查的套接口。 writefds:(可选)指针,指向一组等待可写性检查的套接口。 exceptfds:(可选)指针,指向一组等待错误检查的套接口。 timeout:select()最多等待时间,对...
select tid FROM `join` group by tid order by count(*) desc limit 2; CREATE TABLE `join` ( `id` int(25) NOT NULL auto_increment, `uid` int(25) NOT NULL, `tid` int(25) NOT NULL, PRIMARY KEY (`id`) ) ENGINE=InnoDB DEFAULT CHARSET=utf8 AUTO_INCREMENT=7 ; -- -- 导出表中的数据 `join` -- INSERT INTO `join` VALUES (1, 1, 1); INSERT INTO `join` VALUES (2, 1, 2); INSERT INTO `join` VALUES (3, 2, ...
select系统调用是用来让我们的程序监视多个文件句柄(file descrīptor)的状态变化的。程序会停在select这里等待,直到被监视的文件句柄有某一个或多个发生了状态改变。 文件在句柄在Linux里很多,如果你man某个函数,在函数返回值部分说到成功后有一个文件句柄被创建的都是的,如man socket可以看到“On success, a file descrīptor for the new socket is returned.”而man 2 open可以看到“open() and creat() return the new f...