在Windows窗体C#中更新数据库 [英] Update Database in Windows Form C#

问题描述

此命令可以更新数据库并正常工作吗?

 SqlCommand cmdupdate =新的SqlCommand();
            cmdupdate.Connection = cn;
            cmdupdate.CommandType = CommandType.文本;
            cmdupdate.CommandText = "  +
                "  +
                "  +
                "  +
                "  +
                "  +
                "  +  ;"; 

解决方案

wolfsor写道:

此命令可以更新数据库并正常工作吗?

不，它会失败.您正要在终止Sql语句之前串联一个逗号.看一下代码的最后一段；

 + DATENAME(年份，OrderDate)，" ; "  + DATENAME(年份，OrderDate)，; 

删除最后一个逗号，它将起作用.

当您询问如何更正"该语句时，还有一些补充说明；

• 一个SqlCommand实现IDisposable接口.您最好将其封装在using指令中.
• SqlConnection类具有一种称为"CreateCommand"的工厂方法，可用于为该特定连接创建新命令
• 您的连接过多，以牺牲可读性为代价.示例；
  

   +''+'of'+''

  
  用这种形式会更易读；
  '

的

 +'
Can this command update the database and work?

SqlCommand cmdupdate = new SqlCommand();
            cmdupdate.Connection = cn;
            cmdupdate.CommandType = CommandType.Text;
            cmdupdate.CommandText = "UPDATE Orders2 " +
                " SET Monthname= DATENAME (MONTH, OrderDate)," +
                " Weekname = DATENAME (WEEKDAY, OrderDate) +' '+ 'of' +' '+ DATENAME (MONTH, OrderDate)," +
                " Yearname = DATENAME (YEAR, OrderDate)," +
                " MonthYear = DATENAME (MONTH, OrderDate) + ' '+ DATENAME(YEAR, OrderDate)," +
                " QuarterNum = 'Quarter' + ' ' + DATENAME (QUARTER, OrderDate) +' ' + 'of' + ' ' + DATENAME (YEAR, OrderDate)," +
                " Weeknum = 'Week' + ' ' + DATENAME (WK, OrderDate) +' '+ 'of' +' '+ DATENAME (YEAR, OrderDate)," + ";";
解决方案
wolfsor wrote:
Can this command update the database and work?


Nope, it''ll fail. You''re concatenating a comma just before terminating the Sql statement. Take a look at the last piece of the code;

+ DATENAME (YEAR, OrderDate)," + ";";


That would result in this;

+ DATENAME (YEAR, OrderDate),;


Remove that last comma, and it would work.



Some additional remarks, as you asked how to ''correct'' the statement;



A SqlCommand implements the IDisposable interface. You''d best encapsulate it in a using directive.
The SqlConnection class has a factory-method called "CreateCommand" that you can use to create a new command for that particular connection
You''re concatenating too much, at the expense of readability. Example;

+' ' + 'of' + ' ' 


would be more readable in this form;

+' of '


                        
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