where B_time = null与where B_time is null有什么区别?

where B_time = null与where B_time is null有什么区别? 再给指针变量（*p）赋空值（NULL）时,*p=NULL与p=NULL哪个正确?原因? head==NULL与head->next==NULL区别是什么 while(NULL == pHead)与while(pHead == NULL)有什么差别? SQL中IS NOT NULL与!=NULL是等价的吗同题 selectT_customer.customer_No,customer_Name,customer_Category,customer_State,customer_Tel,customer_InputeDate,trackrecord_DateTime=null,days=null from T_customer where T_customer.customer_No not in(select distinct customer_No from T_trackrecord) 至 C++while循环中p->next!=NULL与p!=NULL的适用范围分别是什么?如题 VB错误,求指导select cangwei,qty,storenu,outofplace from YUCHUKU where chukunu='AA123456' and (cangwei='' or cangwei is null or qty=0 or qty='' or qty is null or storenu='' or storenu is null or outofplace='' or outofplace is null)这句话有问 NULL与变量等于空的区别例如 定义一变量 var a=,这个空的变量与NULL有什么区别? dmm:x=MIN(count[change_y line--;,NULL,NULL); LINKLIST *head = NULL,*t vhdl语言中others=>'0'与others=>NULL的区别 NULL与0有区别吗 =NULL与p->next!=NULL区别?当用循环后（p=p->next）,当p指向最后一个节点时,若使用判断语句判断p!=NULL与p->next!=NULL,此时哪个语句再起作用?它们有啥区别啊? select CNAME=case when CNAME is null then '4' else '1' end from SMPTEL where SMPTEL.Newtel='1585'select CNAME=case when CNAME is null then '456' else '123' end from SMPTEL where SMPTEL.Newtel='158'Newtel 没有158 如何让其显示 456现在 java BufferedReader br = null;是什么意思? if(str1==NULL || substr1==NULL) return -1;嘛意思? NULL ==变量a 和 变量a==NULL ,它们有区别吗?