[转载]双TOP二分法生成分页SQL类(支持MSSQL、ACCESS)

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[转载]双TOP二分法生成分页SQL类(支持MSSQL、ACCESS) – 祭天 – 博客园.

博客开张,先发以前的几个老物件儿,以前写下来的,现在发上来权当记录和分享。
这个类是用来生成分页SQL的,记得那时思考写一个只传一条查询语句就能生成分页SQL的方法,
然后发现了双TOP分页法,不过双TOP法在后半页就很慢,后来一个同学发过来的一篇文章:
2分法-通用存储过程分页(top max模式)版本(性能相对之前的not in版本极大提高)
通过它,发现了还二分法这东东,甚感神奇,不过它是用MAX的方式,逐改为双TOP法。

代码如下:

using System;
using System.Collections.Generic;
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
///
///
记录总数     ///
每页记录数     ///
当前页数     ///
SQL查询语句     ///
排序字段,多个则用“,”隔开     /// 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 sbReverseOrder = 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 ", _safeSql);
sbSql.AppendFormat(" ORDER BY {0} ", 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 ", _safeSql);
sbSql.AppendFormat(" ORDER BY {0} ", sbOriginalOrder.ToString());
sbSql.Append(" ) AS T ");
sbSql.AppendFormat(" ORDER BY {0} ", sbReverseOrder.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 ", _pageSize);
sbSql.Append(" ( ");
sbSql.AppendFormat(" SELECT TOP {0} * ", ((_recordCount % _pageSize) + _pageSize * (pageCount - _pageIndex)));
sbSql.AppendFormat(" FROM ({0}) AS T ", _safeSql);
sbSql.AppendFormat(" ORDER BY {0} ", sbReverseOrder.ToString());
sbSql.Append(" ) AS T ");
sbSql.AppendFormat(" ORDER BY {0} ", sbOriginalOrder.ToString());
}

return sbSql.ToString();
}

///
/// 获取记录总数SQL语句
///
///
限定记录数     ///
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);
}
}

双TOP法相比于NOT IN和MAX法,就是可以传入一条SQL语句来生成分页SQL语句,也可多字段排序;
但是有利也有弊,它要求排序字段必须构成唯一记录,且SELECT后的字段列表中,不允许出现与排序字段同名的字段。
虽然SQL2K5及以上版本已经提供了ROWNUM()来进行分页处理,但是使用SQL2K进行开发的还是较多的。

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