how to get values from sql database by selecting combobox items in c#

Question

I'm trying this coding , what is the error in this coding:

private void comboBox2_SelectedIndexChanged(object sender, EventArgs e)
        {
            SqlConnection con = new SqlConnection("Data Source =TWPL-PC\\SQLEXPRESS;Initial Catalog=TWPLSOFTWARE;Integrated security = True");
            con.Open();
            SqlCommand cmd = new SqlCommand("select ACC_ID ,ACC_TYPE ,ACC_ADD,ACC_CITY ,ACC_STATE ,ACC_COUNTRY ,ACC_TIN_N0 ,ACC_ECC_NO,ACC_RANGE,ACC_DIVISION ,ACC_COMMISS ,ACC_GST_NO ,ACC_CONTACT_PERSON ,ACC_PHONE_NO ,ACC_MOBILE_NO ,ACC_EMAIL ,ACC_PRICE_CODE ,ACC_APPROVAL_STATUS,ACC_PAN_NO from ACCOUNT where ACC_NAME='" + comboBox2.SelectedItem.ToString() + "'", con);
            cmd.Parameters.Add(new SqlParameter("@ACC_NAME", comboBox2.SelectedItem.ToString()));
            SqlDataReader dr = cmd.ExecuteReader();
            while (dr.Read())
            {
                textBox17.Text = dr.GetString(0).ToString();
                comboBox1.SelectedItem = dr.GetString(1).ToString();
                richTextBox1.Text = dr.GetString(2).ToString();
                textBox2.Text = dr.GetString(3).ToString();
                textBox3.Text = dr.GetString(4).ToString();
                textBox4.Text = dr.GetString(5).ToString();
                textBox9.Text = dr.GetString(6).ToString();
                textBox11.Text = dr.GetString(7).ToString();
                textBox13.Text = dr.GetString(8).ToString();
                textBox14.Text = dr.GetString(9).ToString();
                textBox16.Text = dr.GetString(10).ToString();
                textBox12.Text = dr.GetString(11).ToString();
                textBox5.Text = dr.GetString(12).ToString();
                textBox6.Text = dr.GetString(13).ToString();
                textBox8.Text = dr.GetString(14).ToString();
                textBox7.Text = dr.GetString(15).ToString();
                textBox15.Text = dr.GetString(16).ToString();
                //checkBox1.Checked=dr.GetString().ToString();
                textBox10.Text = dr.GetString(18).ToString();

            }                     

        }

this is my problem :

"The data types text and varchar are incompatible in the equal to operator."

Answer 1

You are assing @ACC_NAME variable in your query first, then you are tring to add as a parameter again. Check out SqlCommand.Parameters from MSDN.

Try like this;

SqlCommand cmd = new SqlCommand("select ACC_ID ,ACC_TYPE ,ACC_ADD,ACC_CITY ,ACC_STATE ,ACC_COUNTRY ,ACC_TIN_N0 ,ACC_ECC_NO,ACC_RANGE,ACC_DIVISION ,ACC_COMMISS ,ACC_GST_NO ,ACC_CONTACT_PERSON ,ACC_PHONE_NO ,ACC_MOBILE_NO ,ACC_EMAIL ,ACC_PRICE_CODE ,ACC_APPROVAL_STATUS,ACC_PAN_NO from ACCOUNT where ACC_NAME=@ACC_NAME;", con);
cmd.Parameters.AddWithValue("@ACC_NAME", comboBox2.SelectedItem.ToString()));

Also based on your error message;

The data types text and varchar are incompatible in the equal to operator.

In your database, I think your ACC_NAME column type is text. That's why you are getting an error when you try to assing it in a string. You have two options;

• Change your ACC_NAME column type to nvarchar in your database. Text datatype is deprecated.
• Use LIKE operator instead of = in your WHERE clause. You can't compare against text with the = operator. Try;

where ACC_NAME LIKE @ACC_NAME;

Answer 2

There is no @ACC_NAME parameter in your SQL query. Either modify your query like

SqlCommand cmd = new SqlCommand("select ACC_ID ,ACC_TYPE ,ACC_ADD,ACC_CITY ,ACC_STATE ,ACC_COUNTRY ,ACC_TIN_N0 ,ACC_ECC_NO,ACC_RANGE,ACC_DIVISION ,ACC_COMMISS ,ACC_GST_NO ,ACC_CONTACT_PERSON ,ACC_PHONE_NO ,ACC_MOBILE_NO ,ACC_EMAIL ,ACC_PRICE_CODE ,ACC_APPROVAL_STATUS,ACC_PAN_NO from ACCOUNT where ACC_NAME=@ACC_NAME;", con);

or remove the cmd.Parameters.Add(new SqlParameter("@ACC_NAME", comboBox2.SelectedItem.ToString())); statement.

EDIT :

It seems that comboBox1.SelectedItem = dr.GetString(1).ToString(); is causing the problem. I would suggest using comboBox2.Text = dr.GetString(1).ToString(); or better to set using comboBox2.SelectedIndex

Answer 3

I suppose this is a winform project and the error comes from the

comboBox2.SelectedItem.ToString()

If comboBox2 is bound to a datasource, try to use SelectedValue or SelectedText

Otherwise you can also use the Text property of the Combobox also