Question

我是C＃的新手。我想帮助完成代码以执行查询以返回订单后的行号（货币）。该表具有用户（人名）和货币（其点数）。查询将按货币对数据库进行排序，然后返回该用户的行号（字符串输入）。

表
  用户|货币
  人名| ＃

这是我到目前为止用谷歌搜索。

 public int overallrank(string user)
    {
        String sql = "SELECT (SELECT COUNT(*) FROM " + channel + " AS chan2 WHERE chan2.currency > chan1.currency ) as ChanRank FROM " + channel + " as chan1 WHERE chan1.user = ' " + user + "'";
        cmd = new SQLiteCommand(sql, myDB);
        var result = cmd.ExecuteScalar();
        return result == DBNull.Value ? 0 : (int)result;
    }

Answer 1

正如@juharr在评论中指出的那样，ExecuteScalar期待单行和单列。在该单元格中，您需要从数据库中获取排名。目前，您正在选择chan1中的所有列以及排名。

要获得排名，您可以像这样修改代码：

public long overallrank(string user)
{
    String sql = "SELECT (SELECT COUNT(*) FROM " + channel + " AS chan2 WHERE chan2.currency > chan1.currency ) as ChanRank FROM " + channel + " as chan1 WHERE chan1.user = '" + user +"'";
    using (cmd = new SQLiteCommand(sql, myDB))
    {
       var result = cmd.ExecuteScalar();
       return result == DBNull.Value ? 0L : (long)result;
    }
}

按货币排序后输出为Int行号

1 个答案: