笔记:
--mysql: limit
--oracle:rownum伪列
--伪列:在表结构中不存在的列
--rowid伪列:用于唯一标识一行记录
--rownum伪列:行号
select * from emp;--看不到行号
select e.*,rownum from emp e;--正确的
--rownum:行号是从1开始的,也就是有了1才会有2
--分页
--每页显示2条,显示第2页的数据
--pageIndex:第几页(当前页码)
--pageSize:每页显示的记录数
--startRow:(pageIndex-1)*pageSize==>(2-1)2==>2
--endRow:pageIndex*pageSize==>2*2=4
--select * from emp where rownum>startRow and rownum<=endRow
/*
select * from(
select e.*,rownum from emp e where rownum<=endRow
)tmp
where tmp.rownum>startRow
*/
select e.*,rownum from emp e;
select * from (
select e.*,rownum rn from emp e where rownum<=4
) tmp
where tmp.rn>2;
public class PageBean<T>{
private int pageIndex;//当前页码
private int pageSize;//每页显示的记录数
private int pageCount;//总页码
private int totalCount;//总记录数
private List<T> list;//当前分页查询的数据
public Integer getPageIndex(){
return pageIndex;
}
public void setPageIndex(Integer pageIndex){
if(pageIndex>0){
this.pageIndex = pageIndex;
}else{
this.pageIndex = 1 ;
}
}
public Integer getPageSize() {
return pageSize;
}
public void setPageSize(Integer pageSize) {
this.pageSize = pageSize;
setPageCount();
}
public Integer getPageCount() {
return pageCount;
}
public void setPageCount(){
//pageSize不能等于0
this.pageCount = this.totalCount%thisSize==0?
this.totalCount/this.pageSize:this.totalCount/this.pageSize+1;
}
public Integer getTotalCount() {
return totalCount;
}
public void setTotalCount(Integer totalCount) {
this.totalCount = totalCount;
setPageCount();
}
public List<T> getList() {
return list;
}
public void setList(List<T> list) {
this.list = list;
}
}