Visual C＃SQL数据库选择查询到变量 [英] Visual C# SQL Database Select Query into Variables

问题描述

嘿伙计们，

我正在构建一个查询，它将根据值'RentDue'从数据库中选择数据。我想获得相应的值'id'。鉴于我的代码如下，这将如何实现？

  string  sql =  来自Rooms的SELECT（ID，RentDue） +  其中RentDue =' +  22  +  '）; 
 SqlCommand execsql =  new  SqlCommand（sql，cn）; 
 cn.Open（）; 

另外，我该如何处理多个结果？获得ID后，我会将其附加到RichTextView，我希望每次查询运行时都会有多个结果。



谢谢！

解决方案

0）不要对SQL语句使用字符串连接;使用参数化查询。

1）如果您选择单个值，您可以使用ExecuteScalar

2）如果您选择多个值，那么您将需要其他东西 - - 也许是ExecuteReader。

  string  sql =  来自RentDue = @rentdue的房间的SELECT ID ; 
 SqlCommand execsql =  new  SqlCommand（sql，cn）; 
 execsql.Parameters.AddWithValue（  @ rentdue， 22 ）; 
 cn.Open（）; 
 
 ...  //  你想用它做什么？ 

Hey guys,
I am building a query that will select data from the database based on the value 'RentDue'. I am trying to get the corresponding value 'id'. Given my code below, how will this be possible?

string sql = "SELECT  (ID, RentDue) from Rooms " + "where RentDue = '" + 22 + "')";
                SqlCommand execsql = new SqlCommand(sql, cn);
                cn.Open();

Also, how can I handle multiple results? Once I have obtained the ID, I will appending it to a RichTextView, and I expect there will be more than one result every time the query runs.

Thank you!

解决方案

0) Don't use string concatenation to for an SQL statement; use a parameterized query.
1) If you are selecting a single value you can use ExecuteScalar
2) If you are selecting multiple values, then you will need something else -- perhaps ExecuteReader.

string sql = "SELECT ID from Rooms where RentDue = @rentdue";
SqlCommand execsql = new SqlCommand(sql, cn);
execsql.Parameters.AddWithValue ( "@rentdue" , 22 ) ;
cn.Open();

... // What do you want to do with it?

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