using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;
namespace DAL
{
public class FastPageSql
{
private int allCount; //表中记录总数
private bool isDesc; //排序方式
private string primaryKey; //表的主键
private string orderKey; //排序键
private string selectFields; //要选择的字段
private string queryCondition; //筛选条件
private string tableName; //表名称
private int perPageCount; //每页显示数
private int pageIndex; //显示页的索引
private int totalIndex; //总页数
private int middleIndex; //中间页数;
/// <summary>
///
/// </summary>
/// <param name="allcount">表中记录总数</param>
/// <param name="isdesc">排序方式</param>
/// <param name="primarykey">表的主键</param>
/// <param name="orderkey">排序键</param>
/// <param name="tablename">表名称</param>
/// <param name="perpagecount">每页显示数</param>
/// <param name="pageindex">显示页的索引</param>
/// <param name="selectfields">要选择的字段</param>
/// <param name="querycondition">筛选条件</param>
public FastPageSql(int allcount, bool isdesc, string primarykey, string orderkey, string tablename, int perpagecount, int pageindex, string selectfields, string querycondition)
{
allCount = allcount;
isDesc = isdesc;
primaryKey = primarykey;
orderKey = orderkey;
selectFields = selectfields;
queryCondition = querycondition;
tableName = tablename;
perPageCount = perpagecount;
pageIndex = pageindex;
totalIndex = getTotalIndex();
middleIndex = (int)(totalIndex / 2);
}
private int getTotalIndex()
{
if (allCount % perPageCount > 0)
return (int)(allCount / perPageCount) + 1;
else
return allCount / perPageCount;
}
public string GetFastPageSql()
{
string sql = "";
if (pageIndex <= 1)
{
#region 第一页代码
sql = "select top " + perPageCount + " " + selectFields + " from " + tableName + " " + ((queryCondition != "") ? "where " + queryCondition + "" : "") + " order by " + orderKey + " " + ((isDesc) ? "desc" : "asc") + "";
#endregion
}
else if (1 < pageIndex && pageIndex <= middleIndex)
{
#region 中间页之前
if (primaryKey == orderKey)
sql = "select top " + perPageCount + " " + selectFields + " from " + tableName + " where " + primaryKey + "" + ((isDesc) ? "<" : ">") + "(select " + ((isDesc) ? "min" : "max") + "(" + primaryKey + ") from(select top " + perPageCount * (pageIndex - 1) + " " + primaryKey + " from " + tableName + " " + ((queryCondition != "") ? "where " + queryCondition + "" : "") + " order by " + orderKey + " " + ((isDesc) ? "desc" : "asc") + " )) " + ((queryCondition != "") ? "and " + queryCondition + "" : "") + " order by " + orderKey + " " + ((isDesc) ? "desc" : "asc") + "";
else
sql = "select " + selectFields + " from (select top " + perPageCount + " " + selectFields + " from (select top " + perPageCount * pageIndex + " " + selectFields + " from " + tableName + " " + ((queryCondition != "") ? "where " + queryCondition + "" : "") + " order by " + orderKey + " " + ((isDesc) ? "desc" : "asc") + ") order by " + orderKey + " " + ((isDesc) ? "asc" : "desc") + ") order by " + orderKey + " " + ((isDesc) ? "desc" : "asc") + "";
#endregion
}
else if (middleIndex < pageIndex && pageIndex < totalIndex)
{
#region 中间页到最后页之间
if (primaryKey == orderKey)
sql = "select " + selectFields + " from (select top " + perPageCount + " " + selectFields + " from " + tableName + " where " + primaryKey + "" + ((isDesc) ? ">" : "<") + "(select " + ((isDesc) ? "max" : "min") + "(" + primaryKey + ") from (select top " + (allCount - perPageCount * pageIndex) + " " + primaryKey + " from " + tableName + " " + ((queryCondition != "") ? "where " + queryCondition + "" : "") + " order by " + orderKey + " " + ((isDesc) ? "asc" : "desc") + " )) " + ((queryCondition != "") ? "and " + queryCondition + "" : "") + " order by " + orderKey + " " + ((isDesc) ? "asc" : "desc") + ") order by " + orderKey + " " + ((isDesc) ? "desc" : "asc") + "";
else
sql = "select top " + perPageCount + " " + selectFields + " from (select top " + (allCount - (pageIndex - 1) * perPageCount) + " " + selectFields + " from " + tableName + " " + ((queryCondition != "") ? "where " + queryCondition + "" : "") + " order by " + orderKey + " " + ((isDesc) ? "asc" : "desc") + ") order by " + orderKey + " " + ((isDesc) ? "desc" : "asc") + "";
#endregion
}
else if (pageIndex >= totalIndex)
{
#region 最后页
sql = "select " + selectFields + " from (select top " + (allCount - (totalIndex - 1) * perPageCount) + " " + selectFields + " from " + tableName + " " + ((queryCondition != "") ? "where " + queryCondition + "" : "") + " order by " + orderKey + " " + ((isDesc) ? "asc" : "desc") + ") order by " + orderKey + " " + ((isDesc) ? "desc" : "asc") + "";
#endregion
}
return sql;
}
}
}
来源：https://www.cnblogs.com/gaopin/archive/2012/10/11/2719667.html