SQL delete command?

Question

I am having trouble with a simple DELETE statement in SQL with unexpected results , it seems to add the word to the list??. Must be something silly!. but i cannot see it , t

Answer 1

The @Word should not be in quotes in the sql query.

Not sure why you're trying to add the connection on the end of the sql query either.

Answer 2

See the code below:

String queryForUpdateCustomer = "UPDATE  customer SET cbalance=@txtcustomerblnc WHERE cname='" + searchLookUpEdit1.Text + "'";
            try
            {
                using (SqlCommand command = new SqlCommand(queryForUpdateCustomer, con))
                {

                command.Parameters.AddWithValue("@txtcustomerblnc", txtcustomerblnc.Text);


                con.Open();
                int result = command.ExecuteNonQuery();

                // Check Error
                if (result < 0)
                    MessageBox.Show("Error");

                MessageBox.Show("Record Update of Customer...!", "Message", MessageBoxButtons.OK, MessageBoxIcon.Information);
                con.Close();

                loader();
            }

        }
        catch (Exception ex)
        {
            MessageBox.Show(ex.Message);
            con.Close();
        }

Answer 3

You can also try the following if you don't have access to some of the functionality prescribed above (due, I believe, to older versions of software):

using (var connection = _sqlDbContext.CreatSqlConnection())
{
    using (var sqlCommand = _sqlDbContext.CreateSqlCommand())
    {
        sqlCommand.Connection = connection;
        sqlCommand.CommandText = $"DELETE FROM excludes WHERE word = @word";
        sqlCommand.Parameters.Add(
                            _sqlDbContext.CreateParameterWithValue(sqlCommand, "@word", word));
        connection.Open();
        sqlCommand.ExecuteNonQuery();
    }
}
...

I'm an associate dev. Hence the "I believe" above.

Answer 4

SqlCommand Command = new SqlCommand(
                   "DELETE FROM excludes WHERE word='@word'" +
                     conn);

should be replaced with

SqlCommand Command = new SqlCommand(
                   "DELETE FROM excludes WHERE word='@word'",
                     conn);

Also try by removing single quotes as suggested by others like this

SqlCommand Command = new SqlCommand(
                   "DELETE FROM excludes WHERE word=@word",
                     conn);

Answer 5

See the code below:

private void button4_Click(object sender, EventArgs e)
        {
            String st = "DELETE FROM supplier WHERE supplier_id =" + textBox1.Text;

        SqlCommand sqlcom = new SqlCommand(st, myConnection);
        try
        {
            sqlcom.ExecuteNonQuery();
            MessageBox.Show("delete successful");
        }
        catch (SqlException ex)
        {
            MessageBox.Show(ex.Message);
        }
    }


    private void button6_Click(object sender, EventArgs e)
    {
        String st = "SELECT * FROM supplier";

        SqlCommand sqlcom = new SqlCommand(st, myConnection);
        try
        {
            sqlcom.ExecuteNonQuery();
            SqlDataReader reader = sqlcom.ExecuteReader();
            DataTable datatable = new DataTable();
            datatable.Load(reader);
            dataGridView1.DataSource = datatable;
        }
        catch (SqlException ex)
        {
            MessageBox.Show(ex.Message);
        }
    }

Answer 6

Try removing the single quotes. Also why are you concatenating your SQL string with a connection object (.. word='@word'" + conn)???

Try like this:

try
{
    using (var sc = new SqlConnection(ConnectionString))
    using (var cmd = sc.CreateCommand())
    {
        sc.Open();
        cmd.CommandText = "DELETE FROM excludes WHERE word = @word";
        cmd.Parameters.AddWithValue("@word", word);  
        cmd.ExecuteNonQuery();
    }
}
catch (Exception e)
{
    Box.Text = "SQL error" + e;
}
...

Notice also that because the connection is wrapped in a using block you don't need to Close it in a finally statement. The Dispose method will automatically call the .Close method which will return the connection to the ADO.NET connection pool so that it can be reused.

Another remark is that this IncludeWord method does far to many things. It sends SQL queries to delete records, it updates some textboxes on the GUI and it binds some lists => methods like this should be split in separate so that each method has its own specific responsibility. Otherwise this code is simply a nightmare in terms of maintenance. I would very strongly recommend you to write methods that do only a single specific task, otherwise the code quickly becomes a complete mess.