blocks|key|1028071|text|在现代编程中，有一种趋势是将数据(=模型)与数据的显示方式(=视图)分开。要将视图连接到模型，我们需要一个适配器类:+viewmodel。这三个类统称为MVVM。考虑读点这方面的东西。|type|unstyled|depth|inlineStyleRanges|entityRanges|data|1028072|将模型和视图分开的优点是，您可以将模型重用到其他视图中，您可以更改模型而不必更改视图，也可以更改视图而不更改模型。最后，不需要表单就可以更容易地对模型类进行单元测试。|1028073|我提到MVVM，因为您试图将数据库处理与WinForms混合使用。数据库处理(模型)与如何显示获取的数据无关。|1028074|回到你的问题|offset|length|style|BOLD|1028075|显然，显示获取的数据没有问题(还没有)。因此，让我们关注如何在C#中获取数据库数据。|1028076|主要有两种方法:一种是通过DbConnection和DbCommand使用SQL。另一个常用的方法是使用实体框架和LINQ。|1028077|您提到您已经有了获取数据的SQL。所以我会集中讨论这个方法。如果您对实体框架感兴趣，请考虑阅读实体框架代码，并在电视上没有任何内容的情况下进行一些实验。|1028078|您需要一个方法来创建一个表。由于表是一起工作的，所以我的建议不是创建一个创建一个表的方法，而是创建一个在一个调用中创建数据库中所有表的方法。|1028079|public+void+CreateAllTables()
{
++++const+string+sqlText+=+"Create+if+not+exists+TableCustomers+(
+++++++++Id+int,
+++++++++FirstName+Varchar(30),
+++++++++...|code-block|syntax|javascript|1028080|确切的语法在一定程度上取决于您正在使用的SQL方言:+MicroSoft？MySql？SimpleSQL？嗯，我想你比我更了解Sql文本。关于如何发送此数据库：|1028081|++++using+(var+dbConnection+=+new+DbConnection())
++++{
++++++++using+(DbCommand+dbCommand+=+dbConnection.CreateCommand())
++++++++{
++++++++++++dbCommand.CommandText+=+sqlText;|1028082|现在有几种方法可以执行dbCommand：|1028083|检索项目序列：DbCommand.ExecuteReader|unordered-list-item|CODE|1028084|准确检索一个对象：DbCommand.ExecuteScalar|1028085|只执行，不返回数据：DbCommand.ExecuteNonQuery|1028086|在本例中:我们只执行命令。在与数据库通信之前，我们必须打开dbConnection：|1028087|++++++++++++dbConnection.Open();
++++++++++++dbCommand.ExecuteNonQuery();
++++++++}
++++}
}|1028088|DbCommand.ExecuteNonQuery有一个返回值:受影响的行数。有时，检查这一点以确定是否发生错误是很方便的。|1028089|现在要获取一些数据|1028090|public+IEnumerable<Product>+FetchStudentsByLastName(string+lastName)
{
++++const+string+sqlText+=+"Select+Id,+FirstName,+LastName,+...
++++++++From+tableStudents
++++++++Where+LastName+=+@LastName;"|1028091|请注意，我的SQL以@LastName作为参数！|1028092|开头与CreateTables中相同：|1028093|using+(var+dbConnection+=+new+DbConnection())
{
++++using+(DbCommand+dbCommand+=+dbConnection.CreateCommand())
++++{
++++++++dbCommand.CommandText+=+sqlText;|1028094|要填充参数：|1028095|++++++++//+associate+the+parameter+in+the+SQL+text+with+the+value:
++++++++dbCommand.AddWithValue("@LastName",+lastName);|1028096|现在，我们可以打开dbConnection并执行查询了。我们希望获取几行，所以我们必须使用DbCommand.ExecuteReader|1028097|++++++++dbConnection.Open();
++++++++using+(DbDataReader+dbReader+=+dbCommand.ExecuteReader())
++++++++{|1028098|dbDataReader包含获取的数据。使用DbDataReader.Read查找是否还有行要读取。如果是这样，请使用GetInt32、GetString等来读取每行中的单元格：|1028099|++++++++++++while+(dbReader.Read())
++++++++++++{|1028100|显然有一排。我们选择Id作为0列，FirstName选择为第1列，LastName选择为第2列，等等：|1028101|++++++++++++++++Student+fetchedStudent+=+new+Student
++++++++++++++++{
++++++++++++++++++++Id+=+dbReader.GetInt32(0),++++++++++//+column+0+is+an+Int32
++++++++++++++++++++FirstName+=+dbReader.GetString(1),++//+column+1+is+a+string
++++++++++++++++++++LastName+=+dbReader.GetString(2),
++++++++++++++++++++...
++++++++++++++++}

++++++++++++++++yield+return+fetchedStudent;
++++++++++++}
++++++++}
++++}
}|1028102|要添加一个学生，我们做一些类似的事情:创建DbConnection和DbCommand。用SQL文本和DbCommand填充AddWithParameter。|1028103|不同之处在于:我们不期望返回几行，我们只需要添加的学生会的Id。|1028104|如何返回命令中的Id取决于所使用的SQL方言。在SQLLight中，它应该是这样的：|1028105|const+string+sqlText+=+"INSERT+INTO+tableStudent+(
+++FirstName,+LastName,+...)+Values(@FirstName,+@LastName,+...);
+++SELECT+last_insert_rowid();"|1028106|添加新学生后，此SQL文本将返回学生的Id。|1028107|创建DbConnection和DbCommand。然后：|1028108|dbCommand.CommandText+=+sqlText;
dbCommand.AddWithValue("@FirstName,+firstName);
dbCommand.AddWithValue("@LastName,+lastName);
...|1028109|打开数据库，执行只有一个结果的查询：ExecuteScalar，返回返回的Id作为int：|1028110|dbConnection.Open();
return+(int)dbCommand.ExecuteScalar();|1028111|继续播放|1028112|我已经向您展示了如何使用DbConnection和DbCommand与数据库进行通信。|1028113|我演示了如何向SQL文本添加参数。|1028114|要获取数据行，可以使用ExecuteReader并逐行读取、使用DbReader.Read和DbReader.GetString(colum+number)等。|1028115|我演示了如何在不返回值的情况下执行：DbCommand.ExecuteNonQuery。用于创建表、删除表、更新表中的行、从表中删除行。|1028116|最后，我展示了如何返回一个值：DbCommand.ExecuteScalar。用于在添加新行时返回Id。|1028117|entityMap|0|LINK|mutability|MUTABLE|url|https://www.entityframeworktutorial.net/code-first/what-is-code-first.aspx^0|0|0|0|0|6|0|0|0|1B|6|0|0|0|0|0|0|0|7|N|0|9|N|0|A|P|0|0|0|0|P|0|0|0|A|9|0|0|0|0|0|19|N|0|0|0|C|M|H|1N|8|1W|9|0|0|0|0|1Q|G|0|0|0|0|0|0|0|I|D|0|0|0|0|0|B|D|W|D|1A|W|0|I|P|0|F|N|0^^$0|@$1|2|3|4|5|6|7|3A|8|@]|9|@]|A|$]]|$1|B|3|C|5|6|7|3B|8|@]|9|@]|A|$]]|$1|D|3|E|5|6|7|3C|8|@]|9|@]|A|$]]|$1|F|3|G|5|6|7|3D|8|@$H|3E|I|3F|J|K]]|9|@]|A|$]]|$1|L|3|M|5|6|7|3G|8|@]|9|@]|A|$]]|$1|N|3|O|5|6|7|3H|8|@]|9|@]|A|$]]|$1|P|3|Q|5|6|7|3I|8|@]|9|@$H|3J|I|3K|1|3L]]|A|$]]|$1|R|3|S|5|6|7|3M|8|@]|9|@]|A|$]]|$1|T|3|U|5|V|7|3N|8|@]|9|@]|A|$W|X]]|$1|Y|3|Z|5|6|7|3O|8|@]|9|@]|A|$]]|$1|10|3|11|5|V|7|3P|8|@]|9|@]|A|$W|X]]|$1|12|3|13|5|6|7|3Q|8|@]|9|@]|A|$]]|$1|14|3|15|5|16|7|3R|8|@$H|3S|I|3T|J|17]]|9|@]|A|$]]|$1|18|3|19|5|16|7|3U|8|@$H|3V|I|3W|J|17]]|9|@]|A|$]]|$1|1A|3|1B|5|16|7|3X|8|@$H|3Y|I|3Z|J|17]]|9|@]|A|$]]|$1|1C|3|1D|5|6|7|40|8|@]|9|@]|A|$]]|$1|1E|3|1F|5|V|7|41|8|@]|9|@]|A|$W|X]]|$1|1G|3|1H|5|6|7|42|8|@$H|43|I|44|J|17]]|9|@]|A|$]]|$1|1I|3|1J|5|6|7|45|8|@]|9|@]|A|$]]|$1|1K|3|1L|5|V|7|46|8|@]|9|@]|A|$W|X]]|$1|1M|3|1N|5|6|7|47|8|@$H|48|I|49|J|17]]|9|@]|A|$]]|$1|1O|3|1P|5|6|7|4A|8|@]|9|@]|A|$]]|$1|1Q|3|1R|5|V|7|4B|8|@]|9|@]|A|$W|X]]|$1|1S|3|1T|5|6|7|4C|8|@]|9|@]|A|$]]|$1|1U|3|1V|5|V|7|4D|8|@]|9|@]|A|$W|X]]|$1|1W|3|1X|5|6|7|4E|8|@$H|4F|I|4G|J|17]]|9|@]|A|$]]|$1|1Y|3|1Z|5|V|7|4H|8|@]|9|@]|A|$W|X]]|$1|20|3|21|5|6|7|4I|8|@$H|4J|I|4K|J|17]|$H|4L|I|4M|J|17]|$H|4N|I|4O|J|17]|$H|4P|I|4Q|J|17]]|9|@]|A|$]]|$1|22|3|23|5|V|7|4R|8|@]|9|@]|A|$W|X]]|$1|24|3|25|5|6|7|4S|8|@]|9|@]|A|$]]|$1|26|3|27|5|V|7|4T|8|@]|9|@]|A|$W|X]]|$1|28|3|29|5|6|7|4U|8|@$H|4V|I|4W|J|17]]|9|@]|A|$]]|$1|2A|3|2B|5|6|7|4X|8|@]|9|@]|A|$]]|$1|2C|3|2D|5|6|7|4Y|8|@]|9|@]|A|$]]|$1|2E|3|2F|5|V|7|4Z|8|@]|9|@]|A|$W|X]]|$1|2G|3|2H|5|6|7|50|8|@]|9|@]|A|$]]|$1|2I|3|2J|5|6|7|51|8|@]|9|@]|A|$]]|$1|2K|3|2L|5|V|7|52|8|@]|9|@]|A|$W|X]]|$1|2M|3|2N|5|6|7|53|8|@$H|54|I|55|J|17]]|9|@]|A|$]]|$1|2O|3|2P|5|V|7|56|8|@]|9|@]|A|$W|X]]|$1|2Q|3|2R|5|6|7|57|8|@]|9|@]|A|$]]|$1|2S|3|2T|5|6|7|58|8|@]|9|@]|A|$]]|$1|2U|3|2V|5|6|7|59|8|@]|9|@]|A|$]]|$1|2W|3|2X|5|6|7|5A|8|@$H|5B|I|5C|J|17]|$H|5D|I|5E|J|17]|$H|5F|I|5G|J|17]]|9|@]|A|$]]|$1|2Y|3|2Z|5|6|7|5H|8|@$H|5I|I|5J|J|17]]|9|@]|A|$]]|$1|30|3|31|5|6|7|5K|8|@$H|5L|I|5M|J|17]]|9|@]|A|$]]|$1|32|3|-4|5|6|7|5N|8|@]|9|@]|A|$]]]|33|$34|$5|35|36|37|A|$38|39]]]]

In modern programming there is a tendency to separate your data (= model) from the way the your data is displayed (= view). To connect the view to the model, we need an adapter class: the viewmodel. Together these three classes are abbreviated as MVVM. Consider to read something about this.
The advantage of separating the model and the view, is that you can reuse the model for other views, you can change the model without having to change the view, or change the view without changing the model. Finally, it is way easier to unit test the model classes without needing a form.
I mention MVVM, because you try to mix the database handling with WinForms. The database handling (model) has nothing to do with how you display the fetched data.
Back to your question
Apparently you have no problem displaying the fetched data (yet). So let's focus on how you fetch your database data in C#.
There are two major methods: one is using SQL, via a DbConnection and a DbCommand. The other often used method is using entity framework and LINQ.
You mentioned that you already have the SQL to fetch the data. So I'll focus on that method. If you are interested in entity framework, consider reading <a href="https://www.entityframeworktutorial.net/code-first/what-is-code-first.aspx" rel="nofollow noreferrer">Entity Framework Code First</a> and do some experimenting, when there's nothing on TV.
You want a method to create a table. Since tables are working together, my advice would be not to create a method that creates one table, but create a method that creates all tables of your database in one call.
<pre><code>public void CreateAllTables()
{
 const string sqlText = &quot;Create if not exists TableCustomers (
 Id int,
 FirstName Varchar(30),
 ...
</code></pre>
The exact syntax depends a bit on the SQL dialect that you are using: MicroSoft? MySql? SimpleSQL? Well, I think you know the Sql text better than I do. On to how to send this the database:
<pre><code> using (var dbConnection = new DbConnection())
 {
 using (DbCommand dbCommand = dbConnection.CreateCommand())
 {
 dbCommand.CommandText = sqlText;
</code></pre>
Now there are several methods to execute a dbCommand:
<ul>
<li>Retrieve a sequence of items: <code>DbCommand.ExecuteReader</code></li>
<li>Retrieve exactly one object: <code>DbCommand.ExecuteScalar</code></li>
<li>Execute only, no data returned: <code>DbCommand.ExecuteNonQuery</code></li>
</ul>
In this case: we only execute the command. Before communicating with the database we have to open the dbConnection:
<pre><code> dbConnection.Open();
 dbCommand.ExecuteNonQuery();
 }
 }
}
</code></pre>
<code>DbCommand.ExecuteNonQuery</code> has a return value: the number of affected rows. Sometimes it might be handy to check this to see if errors occurred.
Now to fetch some data
<pre><code>public IEnumerable&lt;Product&gt; FetchStudentsByLastName(string lastName)
{
 const string sqlText = &quot;Select Id, FirstName, LastName, ...
 From tableStudents
 Where LastName = @LastName;&quot;
</code></pre>
Note that my SQL has <code>@LastName</code> as parameter!
The beginning is the same as in CreateTables:
<pre><code>using (var dbConnection = new DbConnection())
{
 using (DbCommand dbCommand = dbConnection.CreateCommand())
 {
 dbCommand.CommandText = sqlText;
</code></pre>
To fill the parameter:
<pre><code> // associate the parameter in the SQL text with the value:
 dbCommand.AddWithValue(&quot;@LastName&quot;, lastName);
</code></pre>
Now we are ready to open the dbConnection and execute the query. We expect to fetch several rows, so we have to use <code>DbCommand.ExecuteReader</code>:
<pre><code> dbConnection.Open();
 using (DbDataReader dbReader = dbCommand.ExecuteReader())
 {
</code></pre>
The <code>dbDataReader</code> contains the fetched data. use <code>DbDataReader.Read</code> to find out if there are still rows to read. If so, use <code>GetInt32</code>, <code>GetString</code> etc to read the cells in each row:
<pre><code> while (dbReader.Read())
 {
</code></pre>
Apparently there is a row. We selected Id as column 0, FirstName as column 1, LastName as column 2, etc:
<pre><code> Student fetchedStudent = new Student
 {
 Id = dbReader.GetInt32(0), // column 0 is an Int32
 FirstName = dbReader.GetString(1), // column 1 is a string
 LastName = dbReader.GetString(2),
 ...
 }

 yield return fetchedStudent;
 }
 }
 }
}
</code></pre>
To add a student we do someting similar: Create the DbConnection and the DbCommand. Fill the DbCommand with the SQL text and <code>AddWithParameter</code>.
The difference is: we don't expect several rows as return, we only want the Id of the added Student.
How to return the Id in the command depends on the SQL dialect that you are using. In SQLLight it would be something like this:
<pre><code>const string sqlText = &quot;INSERT INTO tableStudent (
 FirstName, LastName, ...) Values(@FirstName, @LastName, ...);
 SELECT last_insert_rowid();&quot;
</code></pre>
After adding the new student, this SQL text will return the Id of the student.
Create the DbConnection and the DbCommand. Then:
<pre><code>dbCommand.CommandText = sqlText;
dbCommand.AddWithValue(&quot;@FirstName, firstName);
dbCommand.AddWithValue(&quot;@LastName, lastName);
...
</code></pre>
Open the database, and execute the query with only one result: <code>ExecuteScalar</code>, return the returned Id as an int:
<pre><code>dbConnection.Open();
return (int)dbCommand.ExecuteScalar();
</code></pre>
<h2>Resume</h2>
I've shown you how to communicate with a database using DbConnection and DbCommand.
I showed how to add parameters to your SQL text.
To fetch rows of data use <code>ExecuteReader</code> and Read row by row, using <code>DbReader.Read</code>, and <code>DbReader.GetString(colum number)</code> etc.
I showed how to execute without returning value: <code>DbCommand.ExecuteNonQuery</code>. Used in create table, delete table, update row in table, delete row from table.
And finally, I showed how to return one value: <code>DbCommand.ExecuteScalar</code>. Used to return the Id when adding a new row.

Topic:
Simulate data structures and algorithms of a database management system
Request:
<ul>
<li>Data storage</li>
<li>Query: support Select, Insert, Update query</li>
</ul>
I plan to do it on winform, there are create table, select, delete, update commands just like sql. But I don't know how to write those functions in C#. Does anyone have documents on those basic functions of SQL? please help me.
Can anyone with knowledge of this topic guide me step by step? I really don't know what to do

Datastructure and algorithm

翻译质量差，导致语言生硬或混乱。

没有提供实际的解决方法或示例。

解答不清晰，无法理解或解决问题。

页面排版不美观，阅读体验差。

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主题:模拟数据库管理系统请求的数据结构和算法：数据存储查询:支持选择、插入、更新查询我计划在winform上这样做，这里有创建表、选择、删除、更新命令，就像sql一样。但我不知道如何用C#编写这些函数。有人有关于SQL的这些基本功能的文档吗？请帮帮我。有这方面知识的人能一步一步地指导我吗？我真的不知道该怎么办

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