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ASP.NET getting data from SQL Server

I am trying to get the name of the employee from the database and fill it in the textbox for the respective employee id.
I tried this code but nothing is happening on the page. It just reloads and the textbox (name) is left blank only.
SqlConnection con = new SqlConnection(#"Data Source=DESKTOP-0FUUV7B\SQLEXPRESS;Initial Catalog=EmployeeDetails;Integrated Security=True");
con.Open();
           
SqlCommand cmd = new SqlCommand("select * from ProfessionalDetails where EmpId='"+EmployeeId.Text+"'", con);
          
SqlDataReader da = cmd.ExecuteReader();
while (da.Read())
{
    Name.Text = da.GetValue(1).ToString();
}
            
con.Close();

Better solution is to execute the sql statement through Parameterized value.
The details of that process is given below:
using (SqlConnection con = new SqlConnection(live_connectionString))
{
using (SqlCommand cmd = new SqlCommand("Query", con))
{
con.Open();
cmd.CommandType = CommandType.Text;
cmd.Parameters.AddWithValue("#EmpId", employeeId);
SqlDataAdapter da = new SqlDataAdapter();
da.SelectCommand = cmd;
var ds = new DataSet();
da.Fill(ds);
string? name = ds.Tables[0].Rows[1]["Variable name"].ToString();
Name.Text =name;
};
}
}

As mentioned above in comments, you have lot of issues.
you should use using with the connection to dispose of them.
You should use parameterized queries to avoid SQL injection.
Put your code in try catch so that you can easily identify the root cause of the issue.
Define the connection string in config file three than defining in the c# code.
You don’t need to select all the columns. And please avoid select * in the query, instead just write your column name, as you want to select only one column here.
You can use ExecuteScalar, it’s used when you are expecting single value.
And first make sure that textbox has the expected value when you are calling this query.

As noted, use paramters, and BETTER use STRONG typed paramters.
And no need to use a dataset, this is a single table - so use a datatable.
thus:
string strSQL =
#"select * from ProfessionalDetails where EmpId= #ID";
using (SqlConnection con = new SqlConnection(Properties.Settings.Default.TEST4))
{
using (SqlCommand cmd = new SqlCommand(strSQL, con))
{
con.Open();
cmd.Parameters.Add("#ID", SqlDbType.Int).Value = EmployeeID.Text;
DataTable rstData = new DataTable();
rstData.Load(cmd.ExecuteReader());
if (rstData.Rows.Count > 0)
Name.Text = rstData.Rows[0]["Name"].ToString();
}
}

Connection must be valid and open error in visual studio

I'm trying to show in my datagridview all the registers from a mariadb database, but when I start the code, it appears the errror "Connection must be valid and open error", the code is Here:
I'll be glad if somebody can help me :)

There are two main problems with your code. Firstly you don't associate your connection object with your command object, instead of
MySqlCommand cmd = new MySqlCommand("SELECT * FROM encomendas");
It should be
MySqlCommand cmd = new MySqlCommand("SELECT * FROM encomendas", bdcon);
Also, there is no need to call cmd.ExecuteNonQuery(). It is also advisable to use using blocks on objects that implement IDisposable to ensure they are disposed of correctly, so your full code might be:
var datatable = new DataTable();
using (var connection = new MySqlConnection("connectionstring"))
using (var command = new MySqlCommand("SELECT * FROM encomendas", connection ))
{
connection.Open()'
using (var reader = command.ExecuteReader())
{
datatable.Load(reader);
}
}
// Bind to your grid view
With that being said, if you are looking to fill a DataTable then MySqlDataAdapater() is the simplest approach:
var dt = new DataTable();
using (var adapter = new MySqlDataAdapter("SELECT * FROM encomendas", "ConnectionString"))
{
adapter.Fill(dt);
}
// Bind to your grid view

Delete MysqlCommand cmd = new MySqlCommand("") row and
try it
using (var sqlCommand = new MySqlCommand("SELECT * FROM encomendas", bdcon))
{
MySqlDataReader read = sqlCommand.ExecuteReader();
dt.Load(read);
}
try it

Your object of MysqlCommand must have association with your object MysqlConnection. Obviously your cmd has no business with bdcon, that is the reason why it says "Connection must be valid and open error" when you call the method ```cmd.ExecuteNonQuery().
Here is a similar snippet.
SqlConnection sqlConnection = new SqlConnection();
SqlCommand cmd = sqlConnection.CreateCommand();
//or
SqlCommand cmd = new SqlCommand("sql text", sqlConnection);

Search and display certain table element

I'm trying to search my local database table and simply display all it's columns.
I start my sending in
SearchID("1234");
My code so far:
private static void SearchID(string CostumerID)
{
string conStr = #"Data Source = C:\Users\secwp_000\documents\visual studio 2012\Projects\Module5\Module5\Orderdatabase.sdf";
DataSet ds = new DataSet();
SqlCeConnection con = new SqlCeConnection(conStr);
SqlCeCommand cmd = new SqlCeCommand("SELECT * FROM [Order]", con);
SqlCeDataReader dr = cmd.ExecuteReader();
SqlCeDataAdapter adapt = new SqlCeDataAdapter(cmd);
adapt.Fill(ds, "Order");
while (dr.Read())
{
string str = (string)dr[1];
if (str == CostumerID)
{
Console.WriteLine(str);
}
}
}
Where am I thinking wrong?
It stops on
SqlCeDataReader dr = cmd.ExecuteReader();
saying i don't have a connection. But just sounds wierd, because I've just had connection..

You have to open connection using
If(con.state.toString()=="closed")
con.open();
I observe a fault in your query why are you compare your result after fetch from database.you can directly filter in SQL query
Select * from order where table.customer_Id = customerId

You have a connection but you haven't opened it yet:
con.Open();
adapt.Fill(ds, "Order");
con.Close();
In addition you should use using statements for disposable objects like SqlConnection and SqlCommand to make sure they will be disposed properly:
using(SqlCeConnection con = new SqlCeConnection(conStr))
using(SqlCeCommand cmd = new SqlCeCommand("SELECT * FROM [Order]", con))
{
}

I feel so stupid for not seeing this, haha. And it worked! But it wont display anything from the table,
while (dr.Read())
{
string str = (string)dr[1];
if (str == CostumerID)
{
Console.WriteLine(str);
}
}
Following instructions given to me, there is nothing wrong with this code, and it could display Order with costumerID 1234.

Retrieving value from sql ExecuteScalar()

I have the following:
String sql = "SELECT * FROM Temp WHERE Temp.collection = '" + Program.collection + "'";
SqlConnection conn = new SqlConnection(connString);
SqlCommand cmd = new SqlCommand(sql, conn);
Program.defaultCollection = (String)cmd.ExecuteScalar();
And I want to get the second column after executing the statement. I know it will return only one row with two columns
I have read online that I will have to read each row of the result, is there any other way?

ExecuteScalar gets the first column from the first row of the result set. If you need access to more than that you'll need to take a different approach. Like this:
DataTable dt = new DataTable();
SqlDataAdapater sda = new SqlDataAdapter(sql, conn);
sda.Fill(dt);
Program.defaultCollection = dt.Rows[0]["defaultCollection"];
Now, I realize that the field name may not be defaultCollection, but you can fill that in.
From the MSDN documentation for ExecuteScalar:
Executes the query, and returns the first column of the first row in the result set returned by the query. Additional columns or rows are ignored.
Now, as a final bit of advice, please wrap all ADO.NET objects in a using statement. Like this:
using (SqlConnection conn = new SqlConnection(connString))
using (SqlDataAdapter sda = new SqlDataAdapter(sql, conn))
{
DataTable dt = new DataTable();
sda.Fill(dt);
// do something with `dt`
}
this will ensure they are properly disposed.

And I want to get the second column after executing the statement
It is not possible with execute scalar.
is there any other way
You have 2 options here either to use SqlDataAdapter or SqlDataReader.
For you using DataReader is a recommended approach as you don't need offline data or do other worh
by using SqlDataAdapter
using (SqlConnection c = new SqlConnection(
youconnectionstring))
{
c.Open();
/
using (SqlDataAdapter a = new SqlDataAdapter(sql, c))
{
DataTable t = new DataTable();
a.Fill(t);
if(t.Rows.Count > 0)
{
string text = t.Rows[0]["yourColumn"].ToString();
}
}
}
by using DataREader
using (SqlConnection connection =
new SqlConnection(connectionString))
{
SqlCommand command =
new SqlCommand(sql, connection);
connection.Open();
SqlDataReader reader = command.ExecuteReader();
while (reader.Read())
{
//read data here
string text = reader.GetString(1)
}
reader.Close();
}

SqlCommand.ExecuteScalar() can be used only when the result have just one row and one column.
If you need more than one column to be returned, you should use something like this:
String sql = "SELECT * FROM Temp WHERE Temp.collection = '" + Program.collection + "'";
SqlConnection conn = new SqlConnection(connString);
using(SqlCommand cmd = new SqlCommand(sql, conn))
{
using(SqlDataReader rdr = cmd.ExecuteReader())
{
if(rdr.Read())
{
Program.defaultCollection = (String)rdr["Column1"];
Program.someOtherVar = (String)rdr["Column2"];
}
}
rdr.Close();
}
That will be the fastest way.

You can use a DataReader and read only the first column like:
IDataReader cReader = cmd.ExecuteReader();
if(cReader.Read())
{
string cText = cReader.GetString(1); // Second Column
}

ExecuteScalar only returns one value. You have to make sure your query only returns that value.
String sql = "SELECT temp.defaultCollection FROM Temp WHERE Temp.collection = '" + Program.collection + "'";
On a side note, read on SqlParameter. You don't want to concatenate values like that, you'll have a problem when the collection property contains a quote.

SqlDataAdapter, SqlCommand dropping the leading numbers from string

I am trying to execute a SQL statement with a where clause which looks like
string s2 = "Select * from idtyfile where oysterid=" + id ;
SqlCommand da2 = new SqlCommand(s2, con); or
SqlAdapter da2 = new SqlAdapter(s2, con);
Both of these are failing when I am trying to execute them
da2.ExecuteReader();
the data in ID looks like
ID
43PCOU5T
ZP6RAEJ0
For some reason both of these queries are failing on these kind of data.

You are missing the single quotes in your select command which is what is making your original SELECT fail. However I would like to note that you should always parameterize and encapsulate your SqlCommand / SqlConnection in a using statement. The following would be a cleaner more secure way to solve your problem.
string s2 = "Select * from idtyfile where oysterid=#id";
DataTable myDataTable = new DataTable();
using (SqlConnection conn = new SqlConnection(myConnectionString))
using (SqlCommand cmd = new SqlCommand(s2, conn))
{
cmd.Parameters.AddWithValue("#id", id);
conn.Open();
myDataTable.Load(cmd.ExecuteReader());
}
For some educational resources, you should look at the following links.
MSDN Reference for the using keyword
MSDN Reference for SqlCommand -- Look at the Parameters property.