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From the database I am trying to display a single common name using label please guide me I am a beginner in C#

I am trying to make a feedback form where I want to show the name which is inserted n number of times.
My DataBase has for example 9 duplicate names as feedback was input for that same person 9 times and I want to display it on the result that common name.
Please help me out to complete the code/solution or Correct the code and get the result.
SQL QUERY IS RUNNING PROPERLY IT IS SELECTING THE SINGLE DATA FROM DATABASE BUT HOW TO SHOW THIS ON WEBPAGE
public void cal_F2name()
{
string oracledb = "Data Source=(DESCRIPTION =(ADDRESS = (PROTOCOL = TCP****))(****))(CONNECT_DATA =(SERVER = DEDICATED)(SID = ORCL));";
OracleConnection conn = new OracleConnection(oracledb);
conn.Open();
OracleCommand cmd = new OracleCommand();
cmd.Connection = conn;
OracleDataAdapter da1 = new OracleDataAdapter();
DataTable dt1 = new DataTable();
DataSet ds1 = new DataSet();
cmd.CommandText = "SELECT DISTINCT (F2NAME) FROM CMDC_FEEDBACK WHERE PRG_NAME ='" + cb_prg_name.SelectedValue + "'";
da1.SelectCommand = cmd;
da1.Fill(ds1);
name = Convert.ToString(ds1.Tables[0].Rows[0][0].ToString());
Label58.Text = String.Format("{0:0.00}",name);
conn.Close();
}

try using below code, i have made some change in sql query to get only single record as result.
public void cal_F2name()
{
string oracledb = "Data Source=(DESCRIPTION =(ADDRESS = (PROTOCOL = TCP****))(****))(CONNECT_DATA =(SERVER = DEDICATED)(SID = ORCL));";
OracleConnection conn = new OracleConnection(oracledb);
conn.Open();
OracleCommand cmd = new OracleCommand();
cmd.Connection = conn;
OracleDataAdapter da1 = new OracleDataAdapter();
DataTable dt1 = new DataTable();
DataSet ds1 = new DataSet();
cmd.CommandText = "SELECT max(DISTINCT (F2NAME)) FROM CMDC_FEEDBACK WHERE PRG_NAME ='" + cb_prg_name.SelectedValue + "' AND F2NAME<>'' AND F2NAME IS NOT NULL" ;
da1.SelectCommand = cmd;
da1.Fill(ds1);
name = Convert.ToString(ds1.Tables[0].Rows[0][0].ToString());
Label58.Text = String.Format("{0:0.00}",name);
conn.Close();
}
i have not check but it will work, if you result binding to lable is correct.

Updating Data GridView using the selected value inside the dropdown list

I have a dropdownlist and a gridview.. Dropdown list contains the list of the tables I have in my database. What I want is, when I select a particular table name from the dropdownlist, I want all the columns and data inside that particular table display inside the gridview.
This is my code...
Code for displaying the list of tables inside the dropdown is success.. But to bind the columns and data inside the gridview is not success..
Please Help me...
protected void Page_Load(object sender, EventArgs e)
{
using (SqlConnection con = new SqlConnection("Data Source=.\\SQLEXPRESS;Initial Catalog=Employee;Integrated Security=True"))
{
con.Open();
SqlCommand cmd = new SqlCommand("SELECT table_name FROM INFORMATION_SCHEMA.TABLES", con);
SqlDataAdapter da = new SqlDataAdapter(cmd);
DataSet ds = new DataSet();
da.Fill(ds);
DropDownList1.DataSource = ds;
DropDownList1.DataTextField = "table_name";
DropDownList1.DataValueField = "table_name";
DropDownList1.DataBind();
con.Close();
}
}
protected void DropDownList1_SelectedIndexChanged(object sender, EventArgs e)
{
using (SqlConnection con = new SqlConnection("Data Source=.\\SQLEXPRESS;Initial Catalog=Employee;Integrated Security=True"))
{
con.Open();
SqlCommand cmd = new SqlCommand("SELECT * FROM INFORMATION_SCHEMA.columns where table_name='+ DropDownList1.selecteditem.text +'", con);
SqlDataAdapter da = new SqlDataAdapter(cmd);
DataSet ds = new DataSet();
da.Fill(ds);
GridView1.DataSource = ds;
//+DropDownList1.selecteditem.text +
GridView1.DataBind();
con.Close();
}
}

This is a bad idea on several levels. First you are wide open to SQL injection. Second, you are giving everyone full view access to every column and row of every table.
But the reason you are not getting data is because the select string does not make sense. It should look like this
"SELECT * FROM INFORMATION_SCHEMA.columns where table_name='" + DropDownList1.SelectedValue + "'"
But this is how a proper sql connection should look like.
//create a new datatable
DataTable dt = new DataTable();
//create the string that hold the query including token
string query = "SELECT * FROM INFORMATION_SCHEMA.columns where table_name = #TableName";
//create a new database connection
using (SqlConnection connection = new SqlConnection(ConnectionString))
using (SqlCommand command = new SqlCommand(query, connection))
{
command.CommandType = CommandType.Text;
//replace the token with the correct value
command.Parameters.Add("#TableName", SqlDbType.VarChar).Value = DropDownList1.SelectedValue;
//open the connection
connection.Open();
//load the data of the select into the datatable
dt.Load(command.ExecuteReader());
//bind the datatable to the gridview
GridView1.DataSource = dt;
GridView1.DataBind();
//but you can also skip the datatable and bind directly to the gridview
GridView1.DataSource = command.ExecuteReader();
GridView1.DataBind();
}

Fill combobox from SQL database with specific parameter

I have problem to get specific value from sql server with parameter can anybody explain me why it works on winfom but not on wpf and how i can fix it
my code:
private void UpdateItems()
{
COMBOBOX1.Items.Clear();
SqlConnection conn = new SqlConnection(Properties.Settings.Default.constring.ToString());
SqlDataAdapter da = new SqlDataAdapter("SELECT * FROM CLIENT where cod_cli='some_specific_string'", conn);
DataSet ds = new DataSet();
da.Fill(ds, "CLIENT");
COMBOBOX1.ItemsSource = ds.Tables[0].DefaultView;
COMBOBOX1.DisplayMemberPath = ds.Tables[0].Columns["FR"].ToString();
COMBOBOX1.SelectedValuePath = ds.Tables[0].Columns["FC"].ToString();
}
The program when execute this function crash with error:
System.Data.SqlClient.SqlException: 'Invalid column name
'some_specific_string'.'

the solution is
SqlConnection sqlConnection = new SqlConnection(Properties.Settings.Default.constring.ToString());
{
SqlCommand sqlCmd = new SqlCommand("SELECT * FROM CLIENTS where cod_cli=#cod", sqlConnection);
sqlCmd.Parameters.AddWithValue("#cod", cod_cli.Text);
sqlConnection.Open();
SqlDataReader sqlReader = sqlCmd.ExecuteReader();
while (sqlReader.Read())
{
COMBOBOX1.Items.Add(sqlReader["FR"].ToString());
}
sqlReader.Close();
}
The query doesn't recognize string as parameter but adding as SQL parameter it works.

SqlConnection conn = new SqlConnection(Properties.Settings.Default.constring.ToString());
conn.Open();
SqlDataAdapter da = new SqlDataAdapter("SELECT * FROM CLIENT where cod_cli='some_specific_string'", conn);
DataSet ds = new DataSet();
da.Fill(ds, "CLIENT");
//Populate the combobox
COMBOBOX1.ItemsSource = ds.Tables[0].DefaultView;
COMBOBOX1.DisplayMemberPath = "FR";
COMBOBOX1.SelectedValuePath = "FC";
where "FR" and "FC" are existing columns in your SELECT Query.

how to fill the cells of a DataGridView directly

I want to insert data directly in the cells of a datagrid and then send it to the database , but the rows are not being added with data, they remain empty after the insertion, despite the data appears in the cells.value when I run the code line by line using F11. The database is well linked to the datagrid because when I use textboxes to put the data in the datagrid cells, it works, but it doesn´t work when I put data directly in the cells, through the following code:
public void BD_Conexao()
{
try
{
OdbcConnection con = new OdbcConnection("driver= {MySQL ODBC 5.1 Driver};server=xxxx; database=lic; uid=estagio; password=1234; option = 3 ");
con.Open();
}
catch (Exception ex)
{
Console.WriteLine("Erro na ligação à base de dados. \n{0}", ex.Message);
return;
}
}
public void Consulta()
{
con = new OdbcConnection("driver= {MySQL ODBC 5.1 Driver};server=xxxx; database=lic; uid=estagio; password=1234; option = 3 ");
con.Open();
OdbcCommand Command = con.CreateCommand();
Command.CommandText = "select lojas.Id, lojas.NIF, lojas.Loja, lojas.Bloqueado, lojas.DataFim, lojas.lastupdate, lojas.Nome";
Command.CommandType = CommandType.Text;
Command.Connection = con;
OdbcDataAdapter adapter = new OdbcDataAdapter();
adapter.SelectCommand = Command;
DataSet dataSet = new DataSet();
adapter.Fill(dataSet);
grid_lic.DataSource = dataSet;
grid_lic.DataMember = dataSet.Tables[0].TableName;
}
private void bt_preencher_Click(object sender, EventArgs e)
{
BD_Conexao();
string DataFim = dateTimePicker.Value.ToString("yyyy-MM-dd");
string lastupdate = dateTimePicker2.Value.ToString("yyyy-MM-dd");
Commandtext = "insert into lojas (NIF,Loja,bloqueado, DataFim, lastupdate, Nome) values (#NIF,#Loja,#Bloqueado,#DataFim,#lastupdate,#Nome)";
OdbcCommand Command = new OdbcCommand(Commandtext, con);
Command.CommandType = CommandType.Text;
Command.Parameters.AddWithValue("#NIF", grid_lic.CurrentRow.Cells[1].Value);
Command.Parameters.AddWithValue("#Loja", grid_lic.CurrentRow.Cells[2].Value);
Command.Parameters.AddWithValue("#Bloqueado", checkBox_bloq.Checked);
Command.Parameters.AddWithValue("#DataFim", grid_lic.CurrentRow.Cells[4].Value);
Command.Parameters.AddWithValue("#lastupdate", grid_lic.CurrentRow.Cells[5].Value);
Command.Parameters.AddWithValue("#Nome", grid_lic.CurrentRow.Cells[6].Value);
Command.ExecuteNonQuery();
Consulta();
}
What is wrong?

data gird needs a data source property to fill data, so :
1) Insert all the data in database with your insert statement.
2) Then you need to do something like this to bind your data from database:
string connectionString = "Data Source=.;Initial Catalog=pubs;Integrated Security=True";
string sql = "SELECT * FROM Authors";
SqlConnection connection = new SqlConnection(connectionString);
SqlDataAdapter dataadapter = new SqlDataAdapter(sql, connection);
DataSet ds = new DataSet();
connection.Open();
dataadapter.Fill(ds);
connection.Close();
dataGridView1.DataSource = ds;

C# how to prevent duplicated data in the database?

how am i going prevent "lesson Title" from duplicating in database when user input duplicate data?
SqlConnection cnn = new SqlConnection();
SqlCommand cmd = new SqlCommand();
SqlDataAdapter da = new SqlDataAdapter();
SqlCommandBuilder cb = new SqlCommandBuilder(da);
DataSet ds = new DataSet();
cnn.ConnectionString = System.Configuration.ConfigurationManager.ConnectionStrings["Project1ConnectionString"].ConnectionString;
cnn.Open();
cmd.CommandText = "select * from Lesson";
cmd.Connection = cnn;
da.SelectCommand = cmd;
da.Fill(ds, "Lesson");
DataRow drow = ds.Tables["Lesson"].NewRow();
drow["TopicID"] = DropDownList1.Text;
drow["LessonTitle"] = TextBox1.Text;
drow["LessonDate"] = DateTime.Now;
ds.Tables["Lesson"].Rows.Add(drow);
da.Update(ds, "Lesson");

That kind of uniqueness should be enforced by the database. Add a unique constraint to your table:
CREATE UNIQUE INDEX UK_Lesson_Title ON Lesson (Title)

You can create a function to check the duplicate LessonTitle.
Explanantion: here i have created a function called checkDuplicateTitle().
this function takes AllRows of a LessonTable as DataRowCollection and LessonTitle to be verified as inputs.
it will check the LessonTitle of each and every row.
if given LessonTitle is matched with existing Titles from Table then this function returns true else returns false.
if the returned value is true we will ignore the updating the table with new row as LessonTitle is already Existing otherwise we will add it.
Code as below:
void UpdateLessonTable()
{
SqlConnection cnn = new SqlConnection();
SqlCommand cmd = new SqlCommand();
SqlDataAdapter da = new SqlDataAdapter();
SqlCommandBuilder cb = new SqlCommandBuilder(da);
DataSet ds = new DataSet();
cnn.ConnectionString = System.Configuration.ConfigurationManager.ConnectionStrings["Project1ConnectionString"].ConnectionString;
cnn.Open();
cmd.CommandText = "select * from Lesson";
cmd.Connection = cnn;
da.SelectCommand = cmd;
da.Fill(ds, "Lesson");
if (!checkDuplicateTitle(ds.Tables["Lesson"].Rows, textBox1.Text.ToString()))
{
DataRow drow = ds.Tables["Lesson"].NewRow();
drow["TopicID"] = DropDownList1.Text;
drow["LessonTitle"] = TextBox1.Text;
drow["LessonDate"] = DateTime.Now;
ds.Tables["Lesson"].Rows.Add(drow);
da.Update(ds, "Lesson");
}
else
{
//you can display some warning here
// MessageBox.Show("Duplicate Lesson Title!");
}
}
//function for checking duplicate LessonTitle
bool checkDuplicateTitle(DataRowCollection rowTitle,String newTitle)
{
foreach (DataRow row in rowTitle)
{
if(row["LessonTitle"].Equals(newTitle))
return true;
}
return false;
}