Develop Reference

How to Query Return Value on using Compact SQL Command?

I using a compact database created on visual studio. just for a stand alone system with it's database intact already although i'm stuck here in using a select query that could retrieve a boolean if the user exist on the database and also then return it's ID and Username if the user entry exist. can i ask for help regarding on this one.. I am a student trying to learn c# on using compact database.
private void btnLogin_Click(object sender, EventArgs e)
{
try
{
if (!IsEmpty())
{
if (!IsLenght())
{
using (SqlCeConnection con = new SqlCeConnection("Data Source=" +
System.IO.Path.Combine(Path.GetDirectoryName(System.Reflection.Assembly.GetEntryAssembly().Location), "INCdb.sdf")))
{
con.Open();
SqlCeCommand cmd = con.CreateCommand();
cmd.CommandText = "SELECT * FROM LoginTB Where username=#user1 AND password=#pass1";
cmd.Parameters.AddWithValue("#user1", UserTxt.Text.Trim());
cmd.Parameters.AddWithValue("#pass1", PassTxt.Text.Trim());
cmd.CommandType = CommandType.Text;
validlogin = (bool)cmd.ExecuteScalar();
con.Close();
MessageBox.Show(validlogin.ToString());
if (validlogin == true)
{
// cmd. return value ID
// cmd. return value Username
//SysMain Mn = new SysMain();
//Mn.ShowDialog();
//this.Hide();
}
}
}
}
}
catch (Exception ex)
{
gbf.msgBox(1, ex.Message.ToString(), "");
}
}

The code below is probably better, unless there is something special and unstated about the schema of LoginTB.
// ...
var validLogin = false;
using (SqlCeConnection con = new SqlCeConnection(
"Data Source=" +
System.IO.Path.Combine(
Path.GetDirectoryName(
System.Reflection.Assembly.GetEntryAssembly().Location),
"INCdb.sdf")))
{
con.Open();
SqlCeCommand cmd = con.CreateCommand();
cmd.CommandText =
"SELECT COUNT(*) FROM LoginTB Where username=#user1 AND password=#pass1";
cmd.Parameters.AddWithValue("#user1", UserTxt.Text.Trim());
cmd.Parameters.AddWithValue("#pass1", PassTxt.Text.Trim());
cmd.CommandType = CommandType.Text;
validlogin = ((int)cmd.ExecuteScalar()) > 0;
}
MessageBox.Show(validlogin.ToString());
// ...
Note the use of COUNT

insert into a ms access database

i'm realising a litel program with windows forms c#, that saves data in ms ACCESS database.
i write this code
OleDbConnection connect = new OleDbConnection();
private void button1_Click(object sender, EventArgs e)
{
connect.ConnectionString = #"Provider=Microsoft.Jet.OLEDB.4.0;Data Source=C:\Users\Zied\Documents\Visual Studio 2010\Projects\testerMSAcceess\testerMSAcceess\bin\Debug\zimed.mdb";
string fname = textBox1.Text;
string lname = textBox2.Text;
connect.Open();
OleDbCommand cmd = new OleDbCommand(" INSERT INTO user ([nom],[prenom]) VALUES (#fname,#lname)",connect);
if (connect.State == ConnectionState.Open)
{
cmd.Parameters.AddWithValue("#fname", fname);
cmd.Parameters.AddWithValue("#lname", lname);
cmd.ExecuteNonQuery();
MessageBox.Show("ajout ok ");
connect.Close();
try
{
cmd.ExecuteNonQuery();
MessageBox.Show("ajout ok ");
connect.Close();
}
catch (Exception ex)
{
MessageBox.Show("erreur" + ex.Source);
connect.Close();
}
}
else
{
MessageBox.Show("probleme connection");
}
}
and i got this error when executing it
"error in insert methode"
i have not idea the error in insert request. have you an idea

Try this. I added the using-statements and [ ]-brackets to the query string.
string fname = textBox1.Text;
string lname = textBox2.Text;
using(OleDbConnection conn = new OleDbConnection(#"Provider=Microsoft.Jet.OLEDB.4.0;Data Source=C:\Users\Zied\Documents\Visual Studio 2010\Projects\testerMSAcceess\testerMSAcceess\bin\Debug\zimed.mdb"))
using(OleDbCommand cmd = new OleDbCommand("INSERT INTO [user] ([nom],[prenom]) VALUES (#fname,#lname)", conn))
{
try
{
conn.Open();
cmd.Parameters.AddWithValue("#fname", fname);
cmd.Parameters.AddWithValue("#lname", lname);
cmd.ExecuteNonQuery();
MessageBox.Show("ajout ok ");
}
catch (Exception ex) { MessageBox.Show("Erreur" + ex.Source); }
finally { if (conn.State == ConnectionState.Open) { conn.Close(); } }
}

The OLE DB .NET Provider uses positional parameters that are marked with a question mark (?) instead of named parameters.So, Try to use ? instead of named parameter. for example.
INSERT INTO [user] ([nom],[prenom]) VALUES (?,?)
comand.Parameters.Add("nom", OleDbType.VarChar).Value = fname;

Delete a row from a SQL Server table

I'm trying to simply delete a full row from my SQL Server database table using a button event. So far none of my attempts have succeeded. This is what I'm trying to do:
public static void deleteRow(string table, string columnName, string IDNumber)
{
try
{
using (SqlConnection con = new SqlConnection(Global.connectionString))
{
con.Open();
using (SqlCommand command = new SqlCommand("DELETE FROM " + table + " WHERE " + columnName + " = " + IDNumber, con))
{
command.ExecuteNonQuery();
}
con.Close();
}
}
catch (SystemException ex)
{
MessageBox.Show(string.Format("An error occurred: {0}", ex.Message));
}
}
}
I keep receiving the error:
A first chance exception of type 'System.Data.SqlClient.SqlException' occurred in System.Data.dll
An error occurred: Operand type clash: text is incompatible with int
All of the columns in the table are of TEXT type. Why cannot I compare the function argument of type string to the columns to find the match? (And then delete the row?)

As you have stated that all column names are of TEXT type, So, there is need to use IDNumber as Text by using single quote around IDNumber.....
public static void deleteRow(string table, string columnName, string IDNumber)
{
try
{
using (SqlConnection con = new SqlConnection(Global.connectionString))
{
con.Open();
using (SqlCommand command = new SqlCommand("DELETE FROM " + table + " WHERE " + columnName + " = '" + IDNumber+"'", con))
{
command.ExecuteNonQuery();
}
con.Close();
}
}
catch (SystemException ex)
{
MessageBox.Show(string.Format("An error occurred: {0}", ex.Message));
}
}
}

Either IDNumber should be an int instead of a string, or if it's really a string, add quotes.
Better yet, use parameters.

Try with paramter
.....................
.....................
using (SqlCommand command = new SqlCommand("DELETE FROM " + table + " WHERE " + columnName + " = " + #IDNumber, con))
{
command.Paramter.Add("#IDNumber",IDNumber)
command.ExecuteNonQuery();
}
.....................
.....................
No need to close connection in using statement

Looks like IDNumber is a string. It needs single quote wrapped around it.
"DELETE FROM " + table + " WHERE " + columnName + " = '" + IDNumber + "'"

You may change the "columnName" type from TEXT to VARCHAR(MAX). TEXT column can't be used with "=".
see this topic

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 suppliers";
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);
}
}

If you are using MySql Wamp. This code work.
string con="SERVER=localhost; user id=root; password=; database=dbname";
public void delete()
{
try
{
MySqlConnection connect = new MySqlConnection(con);
MySqlDataAdapter da = new MySqlDataAdapter();
connect.Open();
da.DeleteCommand = new MySqlCommand("DELETE FROM table WHERE ID='" + ID.Text + "'", connect);
da.DeleteCommand.ExecuteNonQuery();
MessageBox.Show("Successfully Deleted");
}
catch(Exception e)
{
MessageBox.Show(e.Message);
}
}

private void DeleteProductButton_Click(object sender, EventArgs e)
{
string ProductID = deleteProductButton.Text;
if (string.IsNullOrEmpty(ProductID))
{
MessageBox.Show("Please enter valid ProductID");
deleteProductButton.Focus();
}
try
{
string SelectDelete = "Delete from Products where ProductID=" + deleteProductButton.Text;
SqlCommand command = new SqlCommand(SelectDelete, Conn);
command.CommandType = CommandType.Text;
command.CommandTimeout = 15;
DialogResult comfirmDelete = MessageBox.Show("Are you sure you want to delete this record?");
if (comfirmDelete == DialogResult.No)
{
return;
}
}
catch (Exception Ex)
{
MessageBox.Show(Ex.Message);
}
}

SQL delete command?

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 , tried it a few different ways. All the same result so quite confused.
public void IncludeWord(string word)
{
// Add selected word to exclude list
SqlConnection conn = new SqlConnection();
String ConnectionString = "Data Source = dev\\SQLEXPRESS ;" + "Initial Catalog=sml;" + "User id=** ;" + "Password =*;" + "Trusted_Connection=No";
using (SqlConnection sc = new SqlConnection(ConnectionString))
{
try
{
sc.Open();
SqlCommand Command = new SqlCommand(
"DELETE FROM excludes WHERE word='#word'" +
conn);
Command.Parameters.AddWithValue("#word", word);
Command.ExecuteNonQuery();
}
catch (Exception e)
{
Box.Text = "SQL error" + e;
}
finally
{
sc.Close();
}
ExcludeTxtbox.Text = "";
Box.Text = " Word : " + word + " has been removed from the Exclude List";
ExcludeLstBox.AppendDataBoundItems = false;
ExcludeLstBox.DataBind();
}

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.

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);

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.

To debug this, examine the CommandText on the SqlCommand object. Before reading further, you should try this.
The issue comes with adding the single quotes around a string that is parameterized. Remove the single quotes and life is beautiful. :-)
Oh, and your conn is an object and needs a comma, not a +.

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);
}
}

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();
}

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.

How to use UPDATE in ado net

I need to perform an update in a table(Homework). But it is not just replacing an old value with a new one; to the already existing value in the column i have to add(SUM) the new value(the column is of type int).
This is what i did so far but i am stuck:
protected void subscribeButton_Click(object sender, EventArgs e)
{
string txtStudent = (selectedStudentLabel.Text.Split(' '))[0];
int studentIndex = 0;
studentIndex = Convert.ToInt32(txtStudent.Trim());
SqlConnection conn = new SqlConnection("Server=.\\SQLEXPRESS;AttachDbFilename=|DataDirectory|\\Database.mdf;Trusted_Connection=True;User Instance=yes");
conn.Open();
string sql2 = "UPDATE student SET moneyspent = " + ?????? + " WHERE id=" + studentIndex + ";";
SqlCommand myCommand2 = new SqlCommand(sql2, conn);
try
{
conn.Open();
myCommand2.ExecuteNonQuery();
}
catch (Exception ex)
{
Console.WriteLine("Error: " + ex);
}
finally
{
conn.Close();
}
}
What should i add intead of ??? to achieve my goal?
Is it possible to do it this way? I want to avoid using to many queries.

If i understand you correctly (i'm not sure i do) you want something like this:
string sql2 = "UPDATE student SET moneyspent = moneyspent + #spent WHERE id=#id";
SqlCommand myCommand2 = new SqlCommand(sql2, conn);
myCommand2.Parameters.AddWithValue("#spent", 50 )
myCommand2.Parameters.AddWithValue("#id", 1 )
Notice how i've used parameters and not string concatenation, very important!!