c# - 简化非参数化 mysql 查询

Question

下面的 mySql 查询有问题

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

我正在使用此查询来查找特定项目的排名，它工作正常。但是在程序中运行时，我得到必须定义参数 '@curRank' 的 fatal error 。但那是 mysql 语法，那么我怎样才能得到它的参数呢？

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。这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，这会为所有医院提供相同的评级和相同的排名。

如果不想改代码，可以引用这个answer .其实，我会引用相关部分:

I have to add

;Allow User Variables=True

to the connection string