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C# Parameterized query - parameters not being replaced with set value

I'm passing a query and parameter from a WinForm to a database class. The
The code on the Form looks like this:
string selectedComp = "CPSI";
string catsQuery = "SELECT id, category, old_value, old_desc, new_value, new_desc, reference1, reference2 FROM masterfiles.xref WHERE company_name = '#company' ORDER BY category, old_value";
Db categoriesData = new Db();
dgvCategories.DataSource = categoriesData.GetData(catsQuery, selectedComp);
And in my database class my code to populate the datatable/set is this:
public DataTable GetData(string selectQuery, string selectedComp)
{
NpgsqlConnection conn = new NpgsqlConnection(connString);
DataSet ds = new DataSet();
NpgsqlCommand cmd = new NpgsqlCommand(selectQuery, conn);
cmd.Parameters.Add(new NpgsqlParameter("#company", selectedComp));
//cmd.Parameters.AddWithValue("#company", selectedComp);
//cmd.Parameters.Add("#company", NpgsqlDbType.Text);
//cmd.Parameters["#company"].Value = selectedComp;
try
{
conn.Open();
NpgsqlDataAdapter da = new NpgsqlDataAdapter(selectQuery, conn);
conn.Close();
da.Fill(ds);
return ds.Tables[0];
}
}
But putting a breakpoint at NpgsqlDataAdapter da = new NpgsqlDataAdapter(selectQuery, conn);, selecctQuery hasn't changed - the '#company' is still in the query.
What am I missing?

The root problem is that you're passing the query to the data adapter instead of the command. Change
NpgsqlDataAdapter da = new NpgsqlDataAdapter(selectQuery, conn);
to
NpgsqlDataAdapter da = new NpgsqlDataAdapter(cmd);
I would also use using to dispose of all objects, and don't close the connection until the dataset is filled:
using(NpgsqlConnection conn = new NpgsqlConnection(connString))
using(NpgsqlCommand cmd = new NpgsqlCommand(selectQuery, conn))
{
cmd.Parameters.Add(new NpgsqlParameter("company", selectedComp));
conn.Open();
using(NpgsqlDataAdapter da = new NpgsqlDataAdapter(cmd))
{
DataSet ds = new DataSet();
da.Fill(ds);
}
conn.Close();
return ds.Tables[0];
}

Gridview select row to next page C#

I need to fetch the selected row of Gridview in next page.. I'm getting exception at if (condition) that cannot find table 0 so below is my code.help me out.
protected void Page_Load(object sender, EventArgs e)
{
SqlConnection con = new SqlConnection(cs);
String abc = "Select fname,lname,city,address,empid,email,phone,department from employee Where id=" + Request.QueryString["a"];
SqlCommand cmd = new SqlCommand(abc, con);
SqlDataAdapter da = new SqlDataAdapter();
da.SelectCommand = cmd;
DataSet ds = new DataSet();
**if (ds.Tables[0].Rows.Count > 0)** //getting error at this
{
fname.Text = ds.Tables[0].Rows[0]["fname"].ToString();
lname.Text = ds.Tables[0].Rows[0]["lname"].ToString();
ddl1.SelectedItem.Value = ds.Tables[0].Rows[0]["city"].ToString();
address.Text = ds.Tables[0].Rows[0]["address"].ToString();
empid.Text = ds.Tables[0].Rows[0]["empid"].ToString();
email.Text = ds.Tables[0].Rows[0]["email"].ToString();
phone.Text = ds.Tables[0].Rows[0]["phone"].ToString();
DropDownList1.SelectedItem.Value = ds.Tables[0].Rows[0]["department"].ToString();
}
}

Before the line on error You need to fill your dataset
da.Fill(ds, "MyTable")
EDIT :
You also didn't open your connection
SqlConnection con = new SqlConnection(cs);
//Open the connection
con.Open()
String abc = "Select fname,lname,city,address,empid,email,phone,department from employee Where id=" + Request.QueryString["a"];
SqlCommand cmd = new SqlCommand(abc, con);
SqlDataAdapter da = new SqlDataAdapter(cmd);
DataSet ds = new DataSet();
//Fill the dataset
da.Fill(ds, "MyTable")
//Close the connection
con.Close()
...

c# how to use Combobox.Value for a From Clause in a Sql query

Please can you assist me in a very weird request
I am building a form to represent a table in a datagridview.
I want to change the data that is bound to the datagridview when i select a different value in a combobox. I bound the event to a button.
i get an error when i run the code:
An unhandled exception of type 'System.Data.OleDb.OleDbException' occurred in System.Data.dll Additional information: Syntax error in query. Incomplete query clause.
the code i have is as follows.
private void Ok_button3_Click(object sender, EventArgs e)
{
OleDbConnection con = new OleDbConnection(#"Provider = Microsoft.ACE.OLEDB.12.0; Data Source = E:\database.accdb; Persist Security Info =False;");
OleDbCommand cmd = new OleDbCommand("Select * From #name ", con);
cmd.Parameters.AddWithValue("#name", comboBox1.SelectedValue);
cmd.CommandType = CommandType.Text;
OleDbDataAdapter da = new OleDbDataAdapter(cmd);
DataTable dt = new DataTable();
da.Fill(dt);
dt.TableName = "Project";
dataGridView1.DataSource = dt;
}

This code will help you:
private void Ok_button3_Click(object sender, EventArgs e)
{
OleDbConnection con = new OleDbConnection(#"Provider = Microsoft.ACE.OLEDB.12.0; Data Source = E:\database.accdb; Persist Security Info =False;");
OleDbCommand cmd = new OleDbCommand(String.Concat("Select * From ",comboBox1.Text), con);
cmd.CommandType = CommandType.Text;
OleDbDataAdapter da = new OleDbDataAdapter(cmd);
DataTable dt = new DataTable();
da.Fill(dt);
dt.TableName = "Project";
dataGridView1.DataSource = dt;
}

you can not pass table name as parameter. you can build sql based on your value selection in your combobox. replace your code with this code and check.
private void Ok_button3_Click(object sender, EventArgs e)
{
OleDbConnection con = new OleDbConnection(#"Provider = Microsoft.ACE.OLEDB.12.0; Data Source = E:\database.accdb; Persist Security Info =False;");
OleDbCommand cmd = new OleDbCommand(String.Concat("Select * From ",comboBox1.SelectedValue), con);
cmd.CommandType = CommandType.Text;
OleDbDataAdapter da = new OleDbDataAdapter(cmd);
DataTable dt = new DataTable();
da.Fill(dt);
dt.TableName = "Project";
dataGridView1.DataSource = dt;
}

If you use Data Bound Items then use comboBox1.SelectedValue. If you use Unbound Mode then use comboBox1.SelectedItem.
private void Ok_button3_Click(object sender, EventArgs e)
{
OleDbConnection con = new OleDbConnection(#"Provider = Microsoft.ACE.OLEDB.12.0; Data Source = E:\database.accdb; Persist Security Info =False;");
//OleDbCommand cmd = new OleDbCommand("Select * From " + comboBox1.SelectedValue.ToString(), con);
OleDbCommand cmd = new OleDbCommand("Select * From " + comboBox1.SelectedItem.ToString(), con);
cmd.CommandType = CommandType.Text;
OleDbDataAdapter da = new OleDbDataAdapter(cmd);
DataTable dt = new DataTable();
da.Fill(dt);
dt.TableName = "Project";
dataGridView1.DataSource = dt;
}
But not advice this way. You can use stored Procedure.

Try This:
private void Ok_button3_Click(object sender, EventArgs e)
{
OleDbConnection con = new OleDbConnection(#"Provider = Microsoft.ACE.OLEDB.12.0; Data Source = E:\database.accdb; Persist Security Info =False;");
string tableName = comboBox1.SelectedValue;
var builder = new SqlCommandBuilder();
string escapedTableName = builder.QuoteIdentifier(tableName);
OleDbCommand cmd = new OleDbCommand("Select * From " + escapedTableName , con);
cmd.CommandType = CommandType.Text;
OleDbDataAdapter da = new OleDbDataAdapter(cmd);
DataTable dt = new DataTable();
da.Fill(dt);
dt.TableName = "Project";
dataGridView1.DataSource = dt;
}

populating 2 checkedlistbox from 2 different tables in postgresql

From the title above, Im making a windows form in c# where in 2 of my checkedlistbox should populate the values from 2 tables in the database. However, when I tried to run the code, I always get this exception: "Cannot bind to the new value member".
below is my code. if you could find any errors/suggestions, feel free to comment. It would be a big help. thanks!
DataSet ds = new DataSet();
DataTable dt = new DataTable();
DataTable dt2 = new DataTable();
string connstring = ("Server=localhost;Port=5432;User Id=postgres;Password=021393;Database=postgres;");
NpgsqlConnection conn = new NpgsqlConnection(connstring);
NpgsqlCommand cmd = new NpgsqlCommand("SELECT * FROM data_condition", conn);
cmd.CommandType = CommandType.Text;
conn.Open();
NpgsqlDataAdapter da = new NpgsqlDataAdapter(cmd);
dt.TableName = "data_condition";
da.Fill(dt);
checkedListBox1.DataSource = dt;
checkedListBox1.DisplayMember = "conname";
checkedListBox1.ValueMember = "conid";
string[] condition = dt.Rows[0]["conname"].ToString().Split(',');
NpgsqlCommand cmd2 = new NpgsqlCommand("SELECT * FROM data_allergy", conn);
cmd2.CommandType = CommandType.Text;
NpgsqlDataAdapter da2 = new NpgsqlDataAdapter(cmd2);
dt2.TableName = "data_allergy";
da2.Fill(dt2);
checkedListBox2.DataSource = dt2;
checkedListBox2.DisplayMember = "allergyname";
checkedListBox2.ValueMember = "allerygid";
string[] allergy = dt2.Rows[0]["allergyname"].ToString().Split(',');

How to bind data to label in asp.net

I have created a form in asp.net,where i have some textbox, in which I have taken some input which is stored in the database. I have created another page where I have taken the same number of label as the textbox.
I want to show the data in the labels that I last entered.
How can i do that?
Code:
string cs = ConfigurationManager.ConnectionStrings["TrishanConnection"].ConnectionString;
SqlConnection con = new SqlConnection(cs);
SqlDataAdapter da = new SqlDataAdapter("SELECT TOP 1 coil_id FROM CoilDetails ORDER BY coil_id DESC", con);
con.Open();
DataSet ds = new DataSet();
da.Fill(ds);
LabeCoilid.Text = ds.ToString();
LabeCoilid.DataBind();
con.Close();

Try instead of
LabeCoilid.Text = ds.ToString();
this
LabeCoilid.Text = ds.Tables[0].Rows[0][0].ToString();

LabeCoilid.Text = ds.Tables[0].Rows[0]["coil_id"].ToString();
You don't need to call DataBind()

string cs = ConfigurationManager.ConnectionStrings["TrishanConnection"].ConnectionString;
using(SqlConnection con = new SqlConnection(cs))
{
using (SqlDataAdapter da = new SqlDataAdapter("SELECT TOP 1 coil_id FROM CoilDetails ORDER BY coil_id DESC", con))
{
con.Open();
DataSet ds = new DataSet();
DataTable dt = new DataTable();
da.Fill(ds);
dt=ds.Table[0]
}
}
LabeCoilid.Text = dt.Rows[0][0].ToString();
LabeCoilid.DataBind();
con.Close();
You can change the rows and columns by changing dt,Rows[4][8]