Use Database in C#

Question

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 = 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();
 }

What runtime error are you getting?

Oded
– Oded

2011-05-21 15:56:24 +00:00
Commented May 21, 2011 at 15:56 — Oded
– Oded, Commented May 21, 2011 at 15:56

Bala R · Accepted Answer · 2011-05-21 16:12:38Z

3

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();
}

edited May 21, 2011 at 16:12

answered May 21, 2011 at 15:57

Bala R

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7 Comments

Bala R Over a year ago

@Oded Thanks. From all the formatting I've done on stackoverflow, I been using ` instead of ' all over the place.

ha.M.ed Over a year ago

@ Bala R: thanks for your help...I found my mistake in SELECT command! If I want to use another SELECT right after this SELECT and put that into DataGridView2, I have write all these code agian?

ha.M.ed Over a year ago

@ Bala R: Can you explain a little about button2_Click codes? Is it only way to get data from specific column of DataGridView?

Bala R Over a year ago

@ha.M.ed I'm not sure about the question on another select (can you rephrase it?) but the button2_click basically loops through the rows and appends the value in cell[2] for each row to a stringbuilder instance. You can use a for loop if you would like that instead.

ha.M.ed Over a year ago

@ Bala R - I mean when I showed data in DataGridView1, I write cmd.CommandText = "SELECT ID from Table1 WHERE Name = 'Mick' " and put reuslt in DataGridView2 (use same SqlDataAdapter and DataTable objects), DataGridView1 and DataGridView2 show me all rows without any Selection!

|

Louis · Accepted Answer · 2011-05-21 16:00:44Z

0

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'.

answered May 21, 2011 at 16:00

Louis

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1 Comment

Bob Kaufman Over a year ago

Welcome to StackOverflow, Louis! By your own admission, your answer doesn't add anything to the discussion. Perhaps this would be better as a comment on @Bala's answer?

kheya · Accepted Answer · 2011-05-21 16:00:59Z

0

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.

edited May 21, 2011 at 16:00

answered May 21, 2011 at 16:00

kheya

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