如何使用 executeReader() 方法仅检索一个单元格的值

How to use executeReader() method to retrieve the value of just one cell(如何使用 executeReader() 方法仅检索一个单元格的值)

问题描述

我需要执行以下命令并将结果传递给标签.我不知道如何使用 Reader 来做到这一点.有人可以帮帮我吗?

I need to execute the following command and pass the result to a label. I don't know how can i do it using Reader. Someone can give me a hand?

String sql = "SELECT * FROM learer WHERE learer.id = " + index;
SqlCommand cmd = new SqlCommand(sql,conn);
learerLabel.Text = (String) cmd.ExecuteReader();

如您所见，我创建了 SQL 语句并执行了它，但它不起作用.为什么?

As you can see i create the SQL statement and i execute it, but it does not work. Why?

控制台说:

不能隐式 SqlDataReader 到字符串...

Cannot implicitly SqlDataReader to String...

我怎样才能得到想要的结果作为字符串，以便标签可以正确显示它.

How can i get the desired results as String so the label can display it properly.

推荐答案

不建议使用DataReader和Command.ExecuteReader只获取一个 来自数据库的值.相反，您应该使用 Command.ExecuteScalar 如下:

It is not recommended to use DataReader and Command.ExecuteReader to get just one value from the database. Instead, you should use Command.ExecuteScalar as following:

String sql = "SELECT ColumnNumber FROM learer WHERE learer.id = " + index;
SqlCommand cmd = new SqlCommand(sql,conn);
learerLabel.Text = (String) cmd.ExecuteScalar();

<小时>

这里是有关连接到数据库和管理数据的更多信息.

Here is more information about Connecting to database and managing data.

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