Re: mysql delete code error - C# Discussion Boards

N Mohamed rafi19-Mar-22 19:48

19-Mar-22 19:48

DELETE FROM employee WHERE employee_id=@employee_id AND employee_name=@employee_name AND employee_salary-@employee_salary

this code is working but it shows record deleted successfully but in database its not deleted,, what i do?

OriginalGriff19-Mar-22 21:04

19-Mar-22 21:04

Use the debugger.
Put a breakpoint on the ExecuteNonQuery line:

cmd.ExecuteNonQuery();

and when it hits, look closely at exactly what is in the three variables id, name, and salary.
Then go to your MySql management software and run a SELECT to seem how many records match that criteria.
If it's zero, then no rows will be deleted.
Back to Visual studio, and use step over to execute the ExecuteNonQuery line.
Back to the DB management, and run the query again.
How many rows this time?

If it hasn't changed, then go back to your code and look at it really carefully ... does "-" have the same effect as "="?

"I have no idea what I did, but I'm taking full credit for it." - ThisOldTony
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N Mohamed rafi19-Mar-22 23:05

19-Mar-22 23:05

sir, already i put code cmd.executenonquery sir. see my previous coding. but still record not deleting from database

OriginalGriff19-Mar-22 23:35

19-Mar-22 23:35

Do you read anything people tell you, or are you just expecting to be told exactly what to type?

We are trying to teach you how to solve these problems for yourself, by thinking about what you are doing, and looking at what happens - then thinking again about why that wasn't what you expected.

So go back to what I said last time, and read it again. Where in there did I tell you to "put code cmd.executenonquery"? What did I actually tell you to do?

N Mohamed rafi20-Mar-22 0:02

20-Mar-22 0:02

Sir, i have heard and tried what you said, the below coding is here; if i run coding it shows record deleted successfully but still the record not deleting from database

using System;
using System.Collections.Generic;
using System.ComponentModel;
using System.Linq;
using System.Text;
using System.Threading.Tasks;
using System.Configuration;
using System.Windows.Forms;
using System.Data;
using System.Drawing;
using System.Threading.Tasks;
using MySql.Data.MySqlClient;
using System.Data.SqlClient;

private void DisplayData()
{
string connectionString;
MySqlConnection cnn;
connectionString = @"Data Source=localhost;Initial Catalog=testDB;User ID=root;Password=mysql";
cnn = new MySqlConnection(connectionString);
DataTable dt = new DataTable();
adapt = new MySqlDataAdapter("select * from employee", cnn);
adapt.Fill(dt);
dataGridView1.DataSource = dt;
cnn.Open();
cnn.Close();
}
private void ClearData()
{
textBox6.Text = "";
textBox7.Text = "";
textBox8.Text = "";
ID = 0;
}
private void button9_Click(object sender, EventArgs e)
{
if (textBox6.Text!= "" && textBox7.Text != "" && textBox8.Text != "")
{
string connectionString;
MySqlConnection cnn;
connectionString = @"Data Source=localhost;Initial Catalog=testDB;User ID=root;Password=mysql";
cnn = new MySqlConnection(connectionString);
string id = textBox6.Text;
string name = textBox7.Text;
string salary = textBox8.Text;
textBox6.Text = "";
textBox7.Text = "";
textBox8.Text = "";
string query = "DELETE FROM employee WHERE employee_id=@employee_id AND employee_name=@employee_name AND employee_salary-@employee_salary";
using (MySqlCommand cmd = new MySqlCommand(query))
{
cmd.Parameters.AddWithValue("@employee_id", id);
cmd.Parameters.AddWithValue("@employee_name", name);
cmd.Parameters.AddWithValue("@employee_salary", salary);
cmd.Connection = cnn;
cnn.Open();
cmd.ExecuteNonQuery();
MessageBox.Show("Record Deleted Successfully");
cnn.Close();
DisplayData();
ClearData();
}
}
else
{
MessageBox.Show("Please Select Record to Delete");
}
}

OriginalGriff20-Mar-22 0:37

20-Mar-22 0:37

No, you haven't.

Read what I said again ... and then look closely at your code ...

Richard MacCutchan20-Mar-22 2:13

Richard MacCutchan

20-Mar-22 2:13

N Mohamed rafi wrote:
if i run coding it shows record deleted successfully

No it does not.

Your code just displays the message "Record Deleted Successfully", but you have no idea whether it worked or not. If you read the documentation at SqlCommand.ExecuteNonQuery Method (System.Data.SqlClient) | Microsoft Docs[^], you will see that it returns a value. If you do not check that return value, you have no idea if the delete worked. So stop guessing and use the tools that are available to you.

N Mohamed rafi20-Mar-22 2:21

20-Mar-22 2:21

I don't unsderstand what i have to do sir, pls give step procedure

Richard MacCutchan20-Mar-22 2:25

Richard MacCutchan

20-Mar-22 2:25

N Mohamed rafi wrote:
pls give step procedure

1. Learn C#
2. Learn SQL
3. Learn debugging
4. and most important: use the documentation, especially when your code does not work.

You need to understand that copying code from random sites on the internet is not going to teach you how to become a successful developer. It takes time, study, hard work and practice, practice, practice.

N Mohamed rafi20-Mar-22 1:58

20-Mar-22 1:58

Sir, Pls understand i have tried what you said, first i check db has 13rows and now with cmd.ExecuteNonQuery(); this code running it shows record deleted successfully and db has no change, and i removed cmd.ExecuteNonQuery(); this line and run the code it shows the same, so pls change the code and give pls

if (textBox6.Text!= "" && textBox7.Text != "" && textBox8.Text != "")
{
string connectionString;
MySqlConnection cnn;
connectionString = @"Data Source=localhost;Initial Catalog=testDB;User ID=root;Password=mysql";
cnn = new MySqlConnection(connectionString);
string id = textBox6.Text;
string name = textBox7.Text;
string salary = textBox8.Text;
textBox6.Text = "";
textBox7.Text = "";
textBox8.Text = "";
string query = "DELETE FROM employee WHERE employee_id=@employee_id AND employee_name=@employee_name AND employee_salary-@employee_salary";
using (MySqlCommand cmd = new MySqlCommand(query))
{
cmd.Parameters.AddWithValue("@employee_id", id);
cmd.Parameters.AddWithValue("@employee_name", name);
cmd.Parameters.AddWithValue("@employee_salary", salary);
cmd.Connection = cnn;
cnn.Open();
//cmd.ExecuteNonQuery();
MessageBox.Show("Record Deleted Successfully");
cnn.Close();
DisplayData();
ClearData();
}
}
else
{
MessageBox.Show("Please Select Record to Delete");
}
i think if i am doing wrong i dont know about breakpoint how to do that

modified 20-Mar-22 8:04am.

OriginalGriff20-Mar-22 2:33

20-Mar-22 2:33

You really don't pay any attention to what people say, do you? All you want is somebody to fix your problem for you ... without any effort or thinking on your part. Sad, sad, sad ...

So. A massive hint it is then.
Step 1) Look at your code:

DELETE FROM employee WHERE employee_id=@employee_id AND employee_name=@employee_name AND employee_salary-@employee_salary

Step 2) Read this line of my previous post:

Quote:
If it hasn't changed, then go back to your code and look at it really carefully ... does "-" have the same effect as "="?

Step 3) Put (1) and (2) together.

N Mohamed rafi20-Mar-22 2:46

20-Mar-22 2:46

thank you so much, I am really mad, now I understand the error you said very well, thanks a lot, please say like this specific. it was a blender mistake

OriginalGriff20-Mar-22 3:26

20-Mar-22 3:26

Details are important in development: you need to look in order to see what is there - or you don't find your problems.

Pointing out the problem specifically doesn't teach you to do that - it teaches you to reply on others to do it for you, and you can't grew as a developer based on others doing the "hard bits"

Debugging code is something we all do every day - often several times a day, and occasionally over a period of several days! So start learning how to fix a problem: gather evidence on what is happening, compare that with what you expected, and ask yourself "what do I need to know to find out why?"
Then look for that: form an idea as to why it failed, and make a prediction as you what that implies. Then check that - the debugger is a good tool for that - and see if the way you expected the fault to happen checks out.

Asking others without doing that doesn't help you, not in the long run - it just makes you more dependant on others to fix your problems, and that wastes time and make you look worse than you are.
Have a go with the next one, and see how far you can get - it's not as difficult as it sounds if you just think carefully!

N Mohamed rafi20-Mar-22 3:46

20-Mar-22 3:46

Ok sir

N Mohamed rafi20-Mar-22 2:47

20-Mar-22 2:47

pls suggest me i dont know how to mark this thread as solved?

N Mohamed rafi20-Mar-22 3:09

20-Mar-22 3:09

Warning also showing that

CS0414: the field form1.ID is assigned but its value is never used

CS8618 Non nullable field adapt must contain non null value when exiting constructtor consider declaring the field as nullable

using System;
using System.Collections.Generic;
using System.ComponentModel;
using System.Linq;
using System.Text;
using System.Threading.Tasks;
using System.Configuration;
using System.Windows.Forms;
using System.Data;
using System.Drawing;
using System.Threading.Tasks;
using MySql.Data.MySqlClient;
using System.Data.SqlClient;

namespace Basic
{
public partial class Form1 : Form
{
MySqlDataAdapter adapt;
int ID = 0;
public Form1()
{
InitializeComponent();
DisplayData();
}

private void DisplayData()
{
string connectionString;
MySqlConnection cnn;
connectionString = @"Data Source=localhost;Initial Catalog=testDB;User ID=root;Password=mysql";
cnn = new MySqlConnection(connectionString);
DataTable dt = new DataTable();
adapt = new MySqlDataAdapter("select * from employee", cnn);
adapt.Fill(dt);
dataGridView1.DataSource = dt;
cnn.Open();
cnn.Close();
}
private void ClearData()
{
textBox6.Text = "";
textBox7.Text = "";
textBox8.Text = "";
ID = 0;
}

Connection string Error VS to Mysql

Dave Kreskowiak20-Mar-22 4:51

Dave Kreskowiak

20-Mar-22 4:51

You're not listening, and i'm not even entirely sure you even read entire replies to you. YOu're just looking for copy'n'paste code without any work on your part, that's where the problem lies.

Where did those "AND" clauses come from? They're not in the SQL statement I wrote, and they are not needed at all since an ID uniquely identifies records.

Asking questions is a skill
CodeProject Forum Guidelines
Google: C# How to debug code
Seriously, go read these articles.

Dave Kreskowiak

N Mohamed rafi18-Mar-22 20:32

18-Mar-22 20:32

I want to insert table in db and make connection to mysql to vs.

Error for below code is:
System.NullReferenceException: 'Object reference not set to an instance of an object.'

System.Configuration.ConnectionStringSettingsCollection.this[string].get returned null.

using System;
using System.Collections.Generic;
using System.ComponentModel;
using System.Linq;
using System.Text;
using System.Threading.Tasks;
using System.Configuration;
using System.Windows.Forms;
using System.Data;
using System.Drawing;
using System.Threading.Tasks;
using System.Data.SqlClient;

private void button6_Click(object sender, EventArgs e)
{
string id = textBox6.Text;
string name = textBox7.Text;
string salary = textBox8.Text;
textBox6.Text = "";
textBox7.Text = "";
textBox8.Text = "";
string query = "INSERT INTO employee VALUES(@employee_id, @employee_name, @employee_salary)";
string constr = ConfigurationManager.ConnectionStrings["constr"].ConnectionString;
using (SqlConnection con = new SqlConnection(constr))
{
using (SqlCommand cmd = new SqlCommand(query))
{
cmd.Parameters.AddWithValue("@employee_id", id);
cmd.Parameters.AddWithValue("@employee_name", name);
cmd.Parameters.AddWithValue("@employee_salary", salary);
cmd.Connection = con;
con.Open();
cmd.ExecuteNonQuery();
con.Close();
}
}
}

Error for below code is:

System.Data.SqlClient.SqlException: 'A network-related or instance-specific error occurred while establishing a connection to SQL Server. The server was not found or was not accessible. Verify that the instance name is correct and that SQL Server is configured to allow remote connections. (provider: Named Pipes Provider, error: 40 - Could not open a connection to SQL Server)'

private void button8_Click(object sender, EventArgs e)
{
{
string connetionString;
SqlConnection cnn;
connetionString = @"Data Source=LAPTOP-NDOAR92R;Initial Catalog=testDB;User ID=root;Password=mysql";
cnn = new SqlConnection(connetionString);
cnn.Open();
MessageBox.Show("Connection Open!");
cnn.Close();
}
}

OriginalGriff18-Mar-22 21:04

18-Mar-22 21:04

Read the error message, it is not only explicit, it tells you what to do to fix it:

A network-related or instance-specific error occurred while establishing a connection to SQL Server. The server was not found or was not accessible. Verify that the instance name is correct and that SQL Server is configured to allow remote connections. (provider: Named Pipes Provider, error: 40 - Could not open a connection to SQL Server)

This may help: Simple SQL Connection String Creation[^]

N Mohamed rafi18-Mar-22 21:08

18-Mar-22 21:08

ok sir please tell step procedure i am very new to it. i don't know to correct it please help me

modified 19-Mar-22 3:19am.

OriginalGriff18-Mar-22 21:17

18-Mar-22 21:17

1) DON'T SHOUT. Using all capitals is considered shouting on the internet, and rude (using all lower case is considered childish). Use proper capitalization if you want to be taken seriously.

2) How do you expect me to tell you that step by step, given that I can't see your screen, access your HDD, or have a browse around your network? Did you read the link I gave you?

N Mohamed rafi18-Mar-22 21:27

18-Mar-22 21:27

I don't understand that link sir, please send some more article pages

OriginalGriff18-Mar-22 22:35

18-Mar-22 22:35

What part did you not understand?

Let's take the instructions one by one...

Quote:
Create an empty text file somewhere on your hard disk, called "myfile.udl".

Have you done that?

N Mohamed rafi18-Mar-22 22:51