Question

我在下面的mySql查询中遇到问题

SELECT name, hospitalID, currentAvgRating, rank 
FROM ( SELECT name,hospitalID,currentAvgRating,city,
              @curRank := @curRank + 1 AS rank 
       FROM hospitals h, ( SELECT @curRank := 0) r 
       ORDER BY currentAvgRating DESC
      ) toplist 
WHERE toplist.hospitalID = @hospitalID 
  and city = @city

此查询用于查找特定项目的排名＆amp;它运作正常。但是在程序中运行时我必须定义参数'@curRank'的致命错误。但那是mysql语法然后我怎么能得到它的参数？

更新

string str = "SELECT name, hospitalID, currentAvgRating, rank FROM (SELECT name,hospitalID,currentAvgRating,city,@curRank := @curRank + 1 AS rank FROM hospitals h, (SELECT @curRank := 0) r ORDER BY currentAvgRating DESC) toplist WHERE toplist.hospitalID = @hospitalID and city = @city";
con.Open();
MySqlCommand cmd = new MySqlCommand(str, con);
cmd.Parameters.AddWithValue("@hospitalID", generalID.Text);
cmd.Parameters.AddWithValue("@city", cityName.Text);
MySqlDataAdapter da = new MySqlDataAdapter(cmd);
DataTable dt = new DataTable();
da.Fill(dt);
con.Close();

Answer 1

您可以获得没有排名的特定医院/城市对的排名。以下是您的查询的近似值：

select count(*) + 1 as ranking
from hospitals h cross join
     (select h.currentAvgRating
      from hospitals h
      where h.hospitalID = @hospitalID and h.city = @city
     ) hh
where h.currentAvgRating > hh.currentAvgRating;

与您的代码不同，这为所有医院提供了相同的评分，相同的排名。

如果您不想更改代码，请参阅此answer。实际上，我引用了相关部分：

我必须添加
;Allow User Variables=True
连接字符串

Answer 2

你的SQL是正确的我认为有C＃命令参数和mySQL参数

的混淆

尝试像这样修改SQL代码

SELECT name, hospitalID, currentAvgRating, rank 
FROM ( SELECT name,hospitalID,currentAvgRating,city,
              @curRank := @curRank + 1 AS rank 
       FROM hospitals h, ( SELECT @curRank := 0) r 
       ORDER BY currentAvgRating DESC
      ) toplist 
WHERE toplist.hospitalID = ?hospitalID 
  and city = ?city

你喜欢这个

   string str = <Example Above>;
    con.Open();
    MySqlCommand cmd = new MySqlCommand(str, con);
    cmd.Parameters.AddWithValue("?hospitalID", generalID.Text);
    cmd.Parameters.AddWithValue("?city", cityName.Text);
    MySqlDataAdapter da = new MySqlDataAdapter(cmd);
    DataTable dt = new DataTable();
    da.Fill(dt); 
    con.Close();

只需更改C＃命令参数？而不是使用@

简化非参数化的mysql查询

2 个答案: