uusing system.collections.generic;
sing system;
using system.text;
///

/// 构造分页后的sql语句
///

public static class paginghelper
{
///

/// 获取分页sql语句，排序字段需要构成唯一记录
///

///
///
///
/// sql">SQL查询语句
///
/// 分页sql语句
public static string createpagingsql(int _recordcount,int _pagesize,int _pageindex,string _safesql,string _orderfield)
{
//重新组合排序字段，防止有错误
string[] arrstrorders = _orderfield.split(new char[] { ',' },stringsplitoptions.removeemptyentries);
stringbuilder sboriginalorder = new stringbuilder(); //原排序字段
stringbuilder sbreverSEO教程rder = new stringbuilder(); //与原排序字段相反，用于分页
for (int i = 0; i < arrstrorders.length; i++)
{
arrstrorders[i] = arrstrorders[i].trim(); //去除前后空格
if (i != 0)
{
sboriginalorder.append(",");
sbreverSEOrder.append(",");
}
sboriginalorder.append(arrstrorders[i]);

int index = arrstrorders[i].indexof(" "); //判断是否有升降标识
if (index > 0)
{
//替换升降标识，分页所需
bool flag = arrstrorders[i].indexof(" desc",stringcomparison.ordinalignorecase) != -1;
sbreverSEOrder.appendformat("{0} {1}",arrstrorders[i].remove(index),flag ? "asc" : "desc");
}
else
{
sbreverSEOrder.appendformat("{0} desc",arrstrorders[i]);
}
}

//计算总页数
_pagesize = _pagesize == 0 ? _recordcount : _pagesize;
int pagecount = (_recordcount + _pagesize - 1) / _pagesize;

//检查当前页数
if (_pageindex < 1)
{
_pageindex = 1;
}
else if (_pageindex > pagecount)
{
_pageindex = pagecount;
}

stringbuilder sbsql = new stringbuilder();
//第一页时，直接使用top n，而不进行分页查询
if (_pageindex == 1)
{
sbsql.appendformat(" select top {0} * ",_pagesize);
sbsql.appendformat(" from ({0}) as t ",_safesql);
sbsql.appendformat(" order by {0} ",sboriginalorder.tostring());
}
//最后一页时，减少一个top n
else if (_pageindex == pagecount)
{
sbsql.append(" select * from ");
sbsql.append(" ( ");
sbsql.appendformat(" select top {0} * ",_recordcount - _pagesize * (_pageindex - 1));
sbsql.appendformat(" from ({0}) as t ",sbreverSEOrder.tostring());
sbsql.append(" ) as t ");
sbsql.appendformat(" order by {0} ",sboriginalorder.tostring());
}
//前半页数时的分页
else if (_pageindex < (pagecount / 2 + pagecount % 2))
{
sbsql.append(" select * from ");
sbsql.append(" ( ");
sbsql.appendformat(" select top {0} * from ",_pagesize);
sbsql.append(" ( ");
sbsql.appendformat(" select top {0} * ",_pagesize * _pageindex);
sbsql.appendformat(" from ({0}) as t ",sboriginalorder.tostring());
sbsql.append(" ) as t ");
sbsql.appendformat(" order by {0} ",sboriginalorder.tostring());
}
//后半页数时的分页
else
{
sbsql.appendformat(" select top {0} * from ",((_recordcount % _pagesize) + _pagesize * (pagecount - _pageindex)));
sbsql.appendformat(" from ({0}) as t ",sboriginalorder.tostring());
}

return sbsql.tostring();
}

///

/// 获取记录总数sql语句
///

///
/// sql">SQL查询语句
/// 记录总数sql语句
public static string createtopnsql(int _n,string _safesql)
{
return string.format(" select top {0} * from ({1}) as t ",_n,_safesql);
}

///

/// 获取记录总数sql语句
///

/// sql">SQL查询语句
/// 记录总数sql语句
public static string createcountingsql(string _safesql)
{
return string.format(" select count(1) as recordcount from ({0}) as t ",_safesql);
}
}