Question

这是一段jsp的查询代码，麻烦解释下功能是如何实现的，详细一点

sql="";
sql="select top "+page_record+" * from shangpinxinxi where issh='是' and id not in (select top "+((curpage-1)*page_record)+" id from shangpinxinxi where issh='是' order by id desc) ";

if(request.getParameter("bianhao")=="" ||request.getParameter("bianhao")==null ){}else{sql=sql+" and bianhao like '%"+new String(request.getParameter("bianhao").getBytes("8859_1"))+"%'";}
if(request.getParameter("mingcheng")=="" ||request.getParameter("mingcheng")==null ){}else{sql=sql+" and mingcheng like '%"+new String(request.getParameter("mingcheng").getBytes("8859_1"))+"%'";}
if(request.getParameter("leibie")=="所有" ||request.getParameter("leibie")==null ){}else{sql=sql+" and leibie like '%"+new String(request.getParameter("leibie").getBytes("8859_1"))+"%'";}
if(request.getParameter("faburen")=="" ||request.getParameter("faburen")==null ){}else{sql=sql+" and faburen like '%"+new String(request.getParameter("faburen").getBytes("8859_1"))+"%'";}
sql=sql+" order by id desc";
RS_result=connDbBean.executeQuery(sql);
String id="";
String bianhao="";String mingcheng="";String leibie="";String tupian="";String jianjie="";String qijia="";String jiezhishijian="";String faburen="";String issh="";
String addtime="";
int i=0;
while(RS_result.next()){
i=i+1;
id=RS_result.getString("id");

Answer 1

这是一个分页功能，中间的if...else...用处很简单，就是检查页面传来的查询条件的参数，如果不为空就在sql中加入这个查询条件，都是模糊匹配的；
分页的实现方式是，先在表shangpinxinxi中查出page_record条记录，而且这page_record条记录还要排除当前页数以前的那些记录（(curpage-1)*page_record）；

功能就是这样实现，但是用这种方式查询在表记录量很大的情况下就会效率很低