Use Database in C#

I recently write a simple program that use database.

I've created an DB1.MDF and get data from it.

When I try to do Select from its Table (i.e. Table1), it gets run time error!

How I should do that?!

One more question:

I've created Data Grid View and put data in that. Now, how I can for example use column[2] of it (e.g. column[2] in my dataGridView is LastName and I want to save all LastNames in one String).

Here is my Code:

private void button1_Click(object sender, EventArgs e)
{

     SqlConnection conn = new SqlConnection();

     conn.ConnectionString = @"Data Source=.\SQLEXPRESS;
           AttachDbFilename=|DataDirectory|\DB1.mdf;
           Integrated Security=True;User Instance=True";

     conn.Open();

     SqlCommand cmd = new SqlCommand();

     cmd.Connection = conn;

     cmd.CommandText = "SELECT ID, Name, LastName from Table1 WHERE Name == Joe ";

     SqlDataAdapter da = new SqlDataAdapter();

     da.SelectCommand 开发者_如何学JAVA= cmd;

     DataTable dt = new DataTable();
     da.Fill(dt);

     dataGridView1.DataSource = dt;
     conn.Close();
 }

 private void button2_Click(object sender, EventArgs e)
 {
   textBox1.Text = dataGridView1.Columns[0].ToString();
 } 

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The select query should be like this

cmd.CommandText = "SELECT ID, Name, LastName from Table1 WHERE Name = 'Joe'";

And for your second question, you could use something like this

private void button2_Click(object sender, EventArgs e)
{
     StringBuilder builder = new StringBuilder();
     dataGirdView1.Rows.Cast<DataGridViewRow>().ToList()
         .ForEach(r => builder.Append(r.Cells[2].Value));
     textBox1.Text = builder.ToString();
}

---

Bala R has it right, the == operator does not exist in SQL, therefore if your testing for an equality you should use the single = operator. And if you're comparing strings (varchar or nvarchar in SQL) you should put them in single quotes i.e. 'Joe'.

---

This query seems wrong.

SELECT ID, Name, LastName from Table1 WHERE Name == Joe 

Can you try this?

cmd.CommandText = "SELECT ID, Name, LastName from Table1 WHERE Name = 'Joe'"

Also, please post the details of the error message.