论Top与ROW_NUMBER读取第一页的效率问题及拼接sql查询条件

http://www.cnblogs.com/Leo_wl/p/4921799.html

SELECT TOP 30 * FROM users WHERE nID>2000 And nID<50000 ORDER BY nID DESC;

SELECT * FROM (SELECT ROW_NUMBER() OVER(ORDER BY nID asc) AS rownum,* FROM users Where nID>2000 And nID<50000 ) AS D
        WHERE rownum>0 AND rownum<31;
SELECT * FROM (SELECT ROW_NUMBER() OVER(ORDER BY nID asc) AS rownum,* FROM users Where nID>2000 And nID<50000 ) AS D
        WHERE rownum BETWEEN 1 AND 30;

他们的不同之处在于“提取N条记录”的这个操作，Top N和 WHERE rownum>0 AND rownum<31。

它们具体是如何运行我讲不出理论，但是我可以做个比方：

体育老师让我们跑30步的距离，Top N的做法就是跑30步，自己边跑边数；WHERE rownum>0 AND rownum<31 相当于老师在30步的位置花了个标记，你只管死跑，到了那个标记就相当于跑了30步。我想做了标记死跑这个要快点吧，：）

在查询列表时，不要将查询总条数与查询列表数据一起执行，应分开查询，这样效果会提升

        public string GetCommentCountSql(MQueryCommentsReqParam model)
        {
            var sql = string.Empty;
            string where = GetWhereSql(model);
            sql = string.Format(@"SELECT COUNT(1) FROM dbo.VipCommentProduct {0}", where);
            return sql;
        }

        private static string GetWhereSql(MQueryCommentsReqParam model)
        {

            string where = string.Empty;
            var queryItems = new List<string>();

            if (!string.IsNullOrEmpty(model.CommentIds))
            {
                queryItems.Add(model.CommentIds.IndexOf(',') > 0
                    ? string.Format(" Id in ({0})", model.CommentIds)
                    : string.Format(" Id={0}", model.CommentIds));
            }
            else
            {

                //会员号
                if (model.UserId != null && model.UserId > 0)
                {
                    queryItems.Add(string.Format(" UserId={0}", model.UserId));
                }
                //会员昵称
                if (!string.IsNullOrEmpty(model.ShowNickName))
                {
                    queryItems.Add(string.Format(" charindex('{0}',ShowNickName) > 0", model.ShowNickName));
                }
                //订单号
                if (model.OrderId != null && model.OrderId > 0)
                {
                    queryItems.Add(string.Format(" OrderId={0}", model.OrderId));
                }
                //商品查询条件（商品名或商品
                if (!string.IsNullOrEmpty(model.ProductCondition))
                {
                    var regex = new Regex(@"^d+$");    //正则 判断为数字
                    if (regex.IsMatch(model.ProductCondition))
                    {
                        queryItems.Add(string.Format(" ProductId='{0}'", model.ProductCondition));
                    }
                    else  //为字符串
                    {
                        queryItems.Add(string.Format(" ProductName like '%{0}%'", model.ProductCondition));
                    }
                }
                //评论内容
                if (!string.IsNullOrEmpty(model.ContentInfo))
                {
                    queryItems.Add(string.Format(" charindex('{0}',ContentInfo) > 0", model.ContentInfo));
                }
                //评分
                if (model.Score != null && model.Score > 0)
                {
                    queryItems.Add(string.Format(" Score={0}", model.Score));
                }
                //精华,1:精华
                if (model.IsHighLight != null && model.IsHighLight > -1)
                {
                    queryItems.Add(string.Format(" IsHighLight={0}", model.IsHighLight));
                }
                //是否有图
                if (model.HasPic != null && model.HasPic > -1)
                {
                    if (model.HasPic == 0)  //无图
                    {
                        queryItems.Add(" UserImgObj is null");
                    }
                    if (model.HasPic == 1) //有图
                    {
                        queryItems.Add(" UserImgObj is not null");
                    }
                }
                //是否追评
                if (model.HasReComment != null && model.HasReComment > -1)
                {
                    if (model.HasReComment == 0)  //无追评
                    {
                        queryItems.Add(" ParentId =0");
                    }
                    if (model.HasReComment == 1) //有追评
                    {
                        queryItems.Add(" ParentId >0");
                    }
                }
                //审核状态：1:未审核,2:审核通过,3:审核未通过
                if (model.CheckState != null && model.CheckState > 0)
                {
                    queryItems.Add(string.Format(" CheckState={0}", model.CheckState));
                }
                //审核人
                if (!string.IsNullOrEmpty(model.CheckUser))
                {
                    queryItems.Add(string.Format(" CheckUser='{0}'", model.CheckUser));
                }
                //是否回复
                if (model.HasReply != null && model.HasReply > -1)
                {
                    if (model.HasReply == 0)  //未回复
                    {
                        queryItems.Add(" ReplyContent is null");
                    }
                    if (model.HasReply == 1)
                    {
                        queryItems.Add(" ReplyContent is not null");
                    }
                }
                //回复人
                if (!string.IsNullOrEmpty(model.ReplyUser))
                {
                    queryItems.Add(string.Format(" ReplyUser='{0}'", model.ReplyUser));
                }
                if (model.PeriodTimeType != null && model.PeriodTimeType > 0 && (model.StartTime != null || model.EndTime != null))
                {
                    var periodDic = new Dictionary<int?, string>()
                {
                    {1,"CheckTime"},        //审核时间
                    {2,"AddTime"},            //评论时间
                    {3,"ReplyTime"}            //回复时间
                };
                    if (model.StartTime != null && model.EndTime == null)
                    {
                        queryItems.Add(string.Format(" " + periodDic[model.PeriodTimeType] + ">'{0}'", model.StartTime));
                    }
                    if (model.EndTime != null && model.StartTime == null)
                    {
                        queryItems.Add(string.Format(" " + periodDic[model.PeriodTimeType] + "<'{0}'", model.EndTime));
                    }
                    if (model.StartTime != null && model.EndTime != null)
                    {
                        queryItems.Add(string.Format(" (" + periodDic[model.PeriodTimeType] + ">'{0}' and " + periodDic[model.PeriodTimeType] + "<'{1}')", model.StartTime, model.EndTime));
                    }
                }
                
            }

            if (queryItems.Any())
            {
                where = "where " + string.Join(" and ", queryItems.ToArray());
            }
            return where;
        }