Question

我正在做一个大学出勤项目（Winforms，Mysql，C＃）

我想在所有期间列中更新0到P，1到Ab和2到OD。为此我写了一个for循环和三个更新查询。

在一个查询中执行此操作是否有任何可能的想法？

请帮帮我......

 for (int i = 1; i <= 8; i++)
            {
                string period = "Period" + i;
                string t1p = period1;

                command.CommandText = "update attendance_daily_rpt set " + t1p + " = 'P' where " + t1p + " = 0";
                connection.Open();
                command.ExecuteNonQuery();                
                connection.Close();

                command.CommandText = "update attendance_daily_rpt set " + t1p + " = 'Ab' where " + t1p + " = 1";
                connection.Open();
                command.ExecuteNonQuery();
                connection.Close();

                command.CommandText = "update attendance_daily_rpt set " + t1p + " = 'OD' where " + t1p + " = 2";
                connection.Open();
                command.ExecuteNonQuery();
                connection.Close();
            }

提前致谢...

Answer 1

创建一个用于维护映射的表（attendance_daily_rpt_map）：

+-----------+---------+
| FromValue | ToValue |
+-----------+---------+
| 0         | P       |
| 1         | Ab      |
| 2         | OD      |
+-----------+---------+

然后更改您的查询：

UPDATE
    attendance_daily_rpt
    INNER JOIN attendance_daily_rpt_map ON attendance_daily_rpt.t1p = attendance_daily_rpt_map.FromValue
SET
    attendance_daily_rpt.t1p = attendance_daily_rpt_map.ToValue

Answer 2

SQL：

SET t1p = 
CASE t1p
 WHEN '1' THEN 'AB'
 WHEN '2' THEN 'OD' 
END

自己制作C＃字符串;）

Answer 3

可能但它很可能是一个怪物，可能比二十四个单独的目标更新表现更差。除了以下事实之外，我没有看到您当前的解决方案有什么特别的错误：

您可能希望将其作为交易;和
可能没有必要为每个SQL语句关闭和打开连接。

我试着从类似的东西开始：

connection.Open();
// Start transaction with whatever it takes.
for (int i = 1; i <= 8; i++) {
    string t1p = "Period" + i;;
    command.CommandText = "update attendance_daily_rpt set " + t1p
        + " = 'P' where " + t1p + " = '0'";
    command.ExecuteNonQuery();                
    command.CommandText = "update attendance_daily_rpt set " + t1p
        + " = 'Ab' where " + t1p + " = '1'";
    command.ExecuteNonQuery();
    command.CommandText = "update attendance_daily_rpt set " + t1p
        + " = 'OD' where " + t1p + " = '2'";
    command.ExecuteNonQuery();
}
// Commit transaction.
connection.Close();

你也可以简单地将单个语句下载到数组查找中，例如：

string[] vals = new string[] {"P", "Ab", "OD"};
connection.Open();
// Start transaction with whatever it takes.
for (int i = 1; i <= 8; i++) {
    string t1p = "Period" + i;;
    for (int j = 0; j < vals.Length; j++) {
        command.CommandText = "update attendance_daily_rpt set " + t1p
            + " = '" + vals[j] +"' where " + t1p + " = '" + j + "'";
        command.ExecuteNonQuery();                
    }
}
// Commit transaction.
connection.Close();

Answer 4

您可以使用CASE声明

UPDATE
    attendance_daily_rpt
SET
    PeriodX = CASE PeriodX
                 WHEN '0' THEN 'P'
                 WHEN '1' THEN 'Ab'
                 WHEN '2' THEN 'OD'
                 ELSE PeriodX
             END

如何在mysql中简化更新查询？

4 个答案: