Question

我有一个Winforms应用程序，必须将数据从SQL迁移到MySQL。部分功能需要通过添加所需的表来准备目标数据库（并在必要时删除现有表）。

我正在寻找最有效的方法来确定表是否已成功创建。 This question's answer建议执行查询如果成功则返回大于0的整数值。理想情况下，我想执行命令并使用返回值而不是运行另一个查询。这可能吗？

我目前的代码：

MySqlConnection myConnection = new MySqlConnection(ConnectionString);
string sql = @" DROP TABLE IF EXISTS    `sf_root_items`;
                CREATE TABLE            `sf_root_items` (
                                        `ID` varchar(255) NOT NULL,
                                        `LoweredName` varchar(255) DEFAULT NULL,
                                        `MenuName` varchar(255) DEFAULT NULL,
                                        `Title` varchar(255) DEFAULT NULL,
                                        `Description` varchar(255) DEFAULT NULL,
                                        `PageType` varchar(255) DEFAULT NULL,
                                        `ExternalUrl` varchar(255) DEFAULT NULL,
                                        PRIMARY KEY(`ID`)
                                        )";
MySqlCommand cmd;
try
{
    if (myConnection.State != ConnectionState.Open)
    {
        myConnection.Close();
        myConnection.Open();
    }
    cmd = myConnection.CreateCommand();
    cmd.CommandText = sql;
    int output = cmd.ExecuteNonQuery();

    // a value greater than 0 means execution was successful
    if (output > 0)
    {
        DBPrepDone = "Table created";
    }
    else
    {
        DBPrepDone = "There was an error";
    }

    myConnection.Close();
}
catch (Exception ex)
{
    DBPrepDone = ex.ToString();
}

Answer 1

以下是Microsoft站点

的ExecuteNonQuery返回值的说明

https://msdn.microsoft.com/en-us/library/system.data.sqlclient.sqlcommand.executenonquery%28v=vs.110%29.aspx

虽然ExecuteNonQuery没有返回任何行，但任何输出参数或映射到参数的返回值将填充数据。对于 UPDATE，INSERT和DELETE语句，返回值是数字受命令影响的行数。当表上存在触发器时在插入或更新时，返回值包括数量受插入或更新操作影响的行数和受触发器或触发器影响的行。对于所有其他类型的语句，返回值为-1。如果发生回滚，则返回值也是-1。

要使查询有效，您应该添加对现有表的检查，例如

string sql = @" DROP TABLE IF EXISTS    `sf_root_items`;
    CREATE TABLE            `sf_root_items` (
                            `ID` varchar(255) NOT NULL,
                            `LoweredName` varchar(255) DEFAULT NULL,
                            `MenuName` varchar(255) DEFAULT NULL,
                            `Title` varchar(255) DEFAULT NULL,
                            `Description` text,
                            `PageType` varchar(255) DEFAULT NULL,
                            `ExternalUrl` varchar(255) DEFAULT NULL,
                            PRIMARY KEY(`ID`)
                            )";
string sql_check = @" SELECT count(*)
                    FROM information_schema.TABLES
                    WHERE (TABLE_NAME = 'sf_root_items')
                    AND (TABLE_SCHEMA = '" + WP_db.Text +"')";

MySqlCommand cmd;
try
{
    if (myConnection.State != ConnectionState.Open)
    {
        myConnection.Close();
        myConnection.Open();
    }
    cmd = myConnection.CreateCommand();
    cmd.CommandText = sql;
    cmd.ExecuteNonQuery();

    //call check if table was created
    cmd = myConnection.CreateCommand();
    cmd.CommandText = sql_check;
    var test = cmd.ExecuteScalar();
    int output;
    int.TryParse(test.ToString(), out output);

    // a value greater than 0 means execution was successful
    if (output > 0)
    {
        DBPrepDone = "Table 'sf_root_items' has been created";
    }
    else
    {
        DBPrepDone = "There was an error";
    }

    myConnection.Close();
}
catch (Exception ex)
{
    DBPrepDone = ex.ToString();
}

检查表创建是否成功

1 个答案: