是否可以在 MySql 命令中使用 MySql 赋值运算符 (:=)？

Question

我有一个查询在 MySql workbench 中运行良好，但在运行通过 MySqlCommand.ExecuteReader 时产生语法错误 "You have an error in your SQL syntax; check the manual that corresponds to your MySQL server version for the right syntax to use near ':= 0+1 AS Rank, z.* 
FROM(SELECT MemberId, Valu' at line 2"。所讨论的语法是 select（即 SELECT @r := @r + 1）内的变量赋值。我正在使用 .net connector v.6.9.9 以防相关。另外，这是我的连接字符串："server=mymysqlserveraddress;port=3306;database=dbName;user id=username;password=********;Convert Zero Datetime=True;Allow User Variables=true"

我已尝试在连接字符串中设置 Allow User Variables=true，如下所示：Is it possible to use a MySql User Defined Variable in a .NET MySqlCommand?

我寻找了与此匹配的其他问题，但最终只找到了一个相同的问题，但对于 java 中的休眠：How can I use MySQL assign operator(:=) in hibernate native query?

这是在 MySql Workbench 中工作的原始 sql 查询：

SELECT Rank, Value 
FROM (SELECT @r := @r+1 AS Rank, z.* 
      FROM(SELECT MemberId, Value 
           FROM (SELECT Id, MemberId, Value, CreatedDate, EventId 
                 FROM Scores
                 WHERE (LoadTime IS NULL AND EventId = 408)
                 ORDER BY Value DESC
                ) AS sub 
     )z, 
     (SELECT @r:=0)y
)x 
WHERE x.Value<=228000;

408 和 228000 只是示例 - 我的 C# 代码构造字符串，然后通过以下方式将其发送到服务器：

StringBuilder statisticQueryString = new StringBuilder("");
// construct statisticQueryString
using (MySqlCommand cmd = new MySqlCommand(statisticQueryString.ToString(), conn))
{
    cmd.Parameters.AddWithValue("r", 0);

    using (MySqlDataReader rdr = cmd.ExecuteReader(CommandBehavior.SequentialAccess))
    {
        // Iterate through the collection of RankResult items...
    }
}

构造查询示例（我在发送前将最终查询打印到日志中）因上述语法错误而失败：

SELECT Rank, Value 
FROM (SELECT @r := @r+1 AS Rank, z.* 
      FROM(SELECT MemberId, Value 
           FROM (SELECT Id, MemberId, Value, CreatedDate, EventId 
                 FROM Scores
                 WHERE (LoadTime IS NULL AND EventId = 408)
                 ORDER BY Value DESC
                ) AS sub 
     )z, 
     (SELECT @r:=0)y
)x 
WHERE x.Value<=228000;

如您所见，构造的查询与我可以运行在 MySql workbench.

中没有错误的查询相同

Answer 1

@Uueerdo 的评论促使我尝试从 C# 代码中删除 cmd.Parameters.AddWithValue("r", 0); 行。这修复了错误并给了我预期的结果。

是否可以在 MySql 命令中使用 MySql 赋值运算符 (:=)？

Is it possible to use MySql assignment operator (:=) in a MySqlCommand?

.net

c#

mysql

parameters

mysql-connector