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Limiting the number of retrieved rows using Fill in ADOMD

The following C# code runs a DAX statement and retrieves a DataTable. This works fine, but now I need to retrieve from the database up to N rows. Is there a way to limit the number of rows returned by the Fill function? If not, how can I retrieve the top N rows? Note that I need to keep this generic for any DAX statement, so you shouldn't change the DAX itself. Also, I don't want to retrieve all the data and then take the first N rows as the data may be too large.
public static DataTable runDaxStatement(int maxRows) {
var con = ConfigurationManager.ConnectionStrings["Default"].ConnectionString;
AdomdConnection conn = new AdomdConnection(con);
DataSet ds = new DataSet();
ds.EnforceConstraints = false;
AdomdCommand cmd = new AdomdCommand("evaluate customers", conn);
AdomdDataAdapter da = new AdomdDataAdapter(cmd);
da.Fill(ds);
return ds.Tables[0];
}

Came across the following TOPN function in the documentation.
This can be used to return the top N rows of the specified table.
For example
public static DataTable runDaxStatement(int maxRows) {
var connectionString = ConfigurationManager.ConnectionStrings["Default"].ConnectionString;
using(AdomdConnection connection = new AdomdConnection(connectionString)) {
string commandText = $"EVALUATE TOPN({maxRows}, customers, <orderBy_expression_here>)";
AdomdCommand command = connection.CreateCommand();
command.CommandText = commandText;
DataSet dataSet = new DataSet(){
EnforceConstraints = false
}
AdomdDataAdapter adapter = new AdomdDataAdapter(command);
adapter.Fill(dataSet);
return dataSet.Tables[0];
}
}

Add SQL query on button using C#

I created a Windows Forms application in C# and my database in Visual Studio. I want to know how, if it's possible, to sort one of the columns in the table by clicking a button? Or how can I sort this column automatically without using a button?
I've tried to implement this sort in the code below, but it doesn't work :(
private c void button5_Click(object sender, EventArgs e)
{
SqlConnection sqlConnection = new SqlConnection("Here is my connecting string");
SqlCommand myCommand = new SqlCommand("SELECT * FROM [Information] ORDER BY (Перевозчик)", sqlConnection);
sqlConnection.Open();
myCommand.ExecuteNonQuery();
}

As found here: https://www.w3schools.com/sql/sql_orderby.asp
Sine we don't know what you want to oder we can only guess here.
But with the query you could try:
SELECT column1, column2, ...
FROM table_name
ORDER BY column1, column2, ... ASC
In your case:
"SELECT * FROM [Information] ORDER BY (Перевозчик) ASC"
Best would be to use the visual query builder where you can query against your database. When you are happy with your result you can at least be sure that the query is correct.
How you can do that is explained here:
https://www.c-sharpcorner.com/article/connect-to-a-database-from-visual-studio/
Since the sqlconnection and the sqlcommand is disposable you should consider putting it in a using tag, like in this example.
https://learn.microsoft.com/en-us/dotnet/api/system.data.sqlclient.sqlcommand?view=netframework-4.8
private static void ReadOrderData(string connectionString)
{
string queryString =
"SELECT OrderID, CustomerID FROM dbo.Orders;";
using (SqlConnection connection = new SqlConnection(
connectionString))
{
SqlCommand command = new SqlCommand(
queryString, connection);
connection.Open();
using(SqlDataReader reader = command.ExecuteReader())
{
while (reader.Read())
{
Console.WriteLine(String.Format("{0}, {1}",
reader[0], reader[1]));
}
}
}
}
There is 2 way for sort data
1) sorting just data and fill into grid:
DataGridView datagridview1 = new DataGridView(); // for show data
DataTable dt1 = new DataTable(); // have data
DataTable dt2 = new DataTable(); // temp data table
DataRow[] dra = dt1.Select("", "ID DESC");
if (dra.Length > 0)
dt2 = dra.CopyToDataTable();
datagridview1.DataSource = dt2;
2) sort default view that is like of sort with grid column header:
DataGridView datagridview1 = new DataGridView(); // for show data
DataTable dt1 = new DataTable(); // have data
dt1.DefaultView.Sort = "ID DESC";
datagridview1.DataSource = dt1;
I found this solution here:
Sorting rows in a data table
For a listbox you could give this a shot
ArrayList q = new ArrayList();
foreach (object o in listBox4.Items)
q.Add(o);
}
q.Sort();
listBox5.Items.Clear();
foreach(object o in q){
listBox5.Items.Add(o);
}
I found this solution here:
Sorting a list of items in a list box

You need to do ExecuteDatareader then process the result coming from this call. ExecuteNonQuery cannot be used to retrieve data.

Query giving only one result

My query is giving one result only i.e. one word for one URL when it should run for every entry in dt. Here dt is DataTable and contains many rows, url_given is a String. temp is table containing the words to be matched. Can anybody please tell me what is wrong with my query?
wordcount is the name of the table. url_String, word and count are columns.
The purpose of the query is to get the URLs matched with given URL and
their words which are in the list which is temp.
foreach (DataRow row in dt.Rows)
{
// read item
url_given = row["url_String"].ToString();
String qrystring = "select url_String,word,count from wordcount where url_String='" + url_given + "' and word in (select * from temp) ";
dt1 = db.searchandorder(qrystring);
// searchandorder is a call to a function that establishes the db connections and passes the query to the data adapter.
}
Here is my searchandorder function:
public DataTable searchandorder (String sql)
{
conn.Open();
SqlDataAdapter da = new SqlDataAdapter(sql, conn);
DataSet ds = new DataSet();
DataTable dt = new DataTable();
da.Fill( dt);
conn.Close();
Console.Write("table coloumns" + dt.Columns.ToString());
return dt;
}

Your problem comes from the fact you loop overwriting dt1 every time. You need to merge the results not replace them, but I can't say how you would do that without seeing db.searchandorder.
Also you have a very dangerous sql injection attack. If url_given was '; drop table wordcount; -- what would be the query the program will execute on the server? You need to use parameters with your data adapter.
EDIT: So, now that you shown your code, here is how you fix it. Instead of making a new DataTable every single time you pass you make one outside of the loop and pass in the same table every time. TableAdapter does not clear out the table before it fills by default.
private YourFunction(DataTable dt)
{
DataTable dt1 = new DataTable();
foreach (DataRow row in dt.Rows)
{
// read item
url_given = row["url_String"].ToString();
String qrystring = "select url_String,word,count from wordcount where url_String='" + url_given + "' and word in (select * from temp) ";
db.searchandorder(qrystring, dt1);
// searchandorder is a call to a function that establishes the db connections and passes the query to the data adapter.
}
DoSomthingWithResults(dt1);
}
public void searchandorder (String sql, DataTable dt)
{
conn.Open();
SqlDataAdapter da = new SqlDataAdapter(sql, conn);
da.Fill( dt);
conn.Close();
Console.Write("table coloumns" + dt.Columns.ToString());
return dt;
}
Now, that is the bare minimum to make your program work. There are a LOT of other bad practices you are doing.
Don't reuse a connection: Your conn object should be created inside searchandorder and be inside a using statement. Don't worry about making "too many connection", .NET will use connection pooling and reuse old connections.
Use using statments: Anything that implements IDisposable should be in a using statement (unless the item is being returned)
Follow naming standards: There is a set of standards C# code follows, your class searcandhorder should be named SerchAndOrder.
Use Parameters: You are vulnerable to a SQL injection attack use parameters for your data adapters. Not only does it improve safety, it makes your program faster by allowing SQL server to cache the query execution plan.
Here is a version of your program with those fixes applied.
private YourFunction(DataTable dt)
{
DataTable dt1 = new DataTable();
foreach (DataRow row in dt.Rows)
{
// read item
url_given = row["url_String"].ToString();
var parameter = new SqlParameter("#urlGiven", SqlDbType.VarChar, url_given.Length);
parameter.Value = url_given;
String qrystring = "select url_String,word,count from wordcount where url_String=#urlGiven and word in (select * from temp) ";
db.searchandorder(qrystring, dt1, parameter);
// searchandorder is a call to a function that establishes the db connections and passes the query to the data adapter.
}
DoSomthingWithResults(dt1);
}
public void SearchAndOrder (String sql, DataTable dt, params SqlParameter[] parameters)
{
using(var conn = new SqlConnection(_connectionString))
using(var da = new SqlDataAdapter(sql, conn))
{
da.SelectCommand.Parameters.AddRange(parameters);
conn.Open();
da.Fill(dt);
}
Console.Write("table coloumns" + dt.Columns.ToString());
return dt;
}

connect and read .MDB item with C#

Is it possible to connect to a local MDB file and pick a single bit of info out of it ?
I have a table in a .mbd file with a single bit of info in it. I would like to have that record be output into a disabled textbox for a reference. I believe I can get the DB open, and run the query but no idea what I need to read from it.
thanks
var myDataTable = new DataTable();
using (var conection = new OleDbConnection("Provider=Microsoft.JET.OLEDB.4.0;" + "data source=C:\\menus\\newmenus\\menu.mdb;Password=****"))
{
conection.Open();
var query = "Select siteid From n_user";
var adapter = new OleDbDataAdapter(query, conection);
OleDbCommandBuilder oleDbCommandBuilder = new OleDbCommandBuilder(adapter);
}

To simply read a single field on your database table you could use an OleDbDataReader that could loop over the result and return the field required..
var myDataTable = new DataTable();
using (var conection = new OleDbConnection("Provider=Microsoft.JET.OLEDB.4.0;" + "data source=C:\\menus\\newmenus\\menu.mdb;Password=****"))
{
conection.Open();
var query = "Select siteid From n_user";
var command = new OleDbCommand(query, conection);
var reader = command.ExecuteReader();
while(reader.Read())
textBox1.Text = reader[0].ToString();
}
if you have just one record and just one field then a better solution is the method ExecuteScalar
conection.Open();
// A query that returns just one record composed of just one field
var query = "Select siteid From n_user where userid=1";
var command = new OleDbCommand(query, conection);
int result = (int)command.ExecuteScalar(); // Supposing that siteid is an integer
Probably I should also mention that ExecuteScalar returns null if the query doesn't find a match for the userid, so it is better to be careful with the conversion here
object result = command.ExecuteScalar();
if( result != null)
int userID = (int)result;
.....

Yes very possible. Just have the adapter fill the DataTable, also I don't think you'll need the OleDbCommandBuilder.
using (var conection = new OleDbConnection("Provider=Microsoft.JET.OLEDB.4.0;" + "data source=C:\\menus\\newmenus\\menu.mdb;Password=****"))
{
conection.Open();
var query = "Select siteid From n_user";
var adapter = new OleDbDataAdapter(query, conection);
adapter.Fill(myDataTable);
myTextBox.Text = myDataTable.Rows[0][0].ToString();
}
Also I think using ExecuteScalar would be a better solution, but my answer was tailored to the objects you had already instantiated.

You could use OleDbCommand.ExecuteScalar to retrieve a single value. It is returned as an object and you could cast it to the correct type.

Are you looking for stm like this?
OleDbCommand cmd = new OleDbCommand();
OleDbDataReader dr = cmd.ExecuteReader();
while (dr.Read())
{
// read ur stuff here.
}

store select result

i want to extract my table names and save it into variables this is my cod that return 3 answer:student, teacher and score. how can i change it to save these tree table name to 3 variable. thank you.
try
{
SqlDataReader myreader = null;
SqlCommand mycommand = new SqlCommand("select * FROM information_schema.tables WHERE table_type = 'BASE TABLE'", myconnect);
myreader = mycommand.ExecuteReader();
while (myreader.Read())
{
Console.WriteLine(myreader[2].ToString());
}
}

A simple builtin way is using Connection.GetSchema:
using (var con = new System.Data.SqlClient.SqlConnection(conStr))
{
con.Open();
DataTable schemaTable = con.GetSchema("Tables");
IList<string> allTableNames = schemaTable.AsEnumerable()
.Where(r => r.Field<string>("TABLE_TYPE") == "BASE TABLE")
.Select(r => r.Field<string>("TABLE_NAME"))
.ToList();
}
Now you have a List<string> with all table names which you can access via indexer or in a loop or create a comma separated list with string.Join:
string tNames = string.Join(",", allTableNames);
Console.Write("all tables in the given database: " + tNames);

You can use this :
string tableName ="" ; // Variable to stroe the table names
string connectionString = ""; //Your connectionstring
// get records from the table
string commandString =""; //Your query
// create the data set command object
// and the DataSet
SqlDataAdapter DataAdapter =new SqlDataAdapter(commandString, connectionString);
DataSet DataSet = new DataSet( );
// fill the DataSet object
DataAdapter.Fill(DataSet, "Customers");
// Get the one table from the DataSet
DataTable dataTable = DataSet.Tables[0];
// for each row in the table, display the info
foreach (DataRow dataRow in dataTable.Rows)
{
tableName = dataRow[0].tostring();
//...
}

if you want to save the result for future user or a different session then you can use any of the following to methods
first one
use the "insert" query to save the result one by one in the a different table that you would create specially for saving the data
you can put the insert command/statement directly into the for loop
second method
use the xml to store the value very simple and memory friendly

I Have modified #Doctor code to use ArrayList to store number of table name in single variables.
ArrayList alTableName = new ArrayList(); // Variable to stroe the table names
string connectionString = ""; //Your connectionstring
// get records from the table
string commandString =""; //Your query
// create the data set command object
// and the DataSet
SqlDataAdapter DataAdapter =new SqlDataAdapter(commandString, connectionString);
DataSet DataSet = new DataSet( );
// fill the DataSet object
DataAdapter.Fill(DataSet, "Customers");
// Get the one table from the DataSet
DataTable dataTable = DataSet.Tables[0];
// for each row in the table, display the info
foreach (DataRow dataRow in dataTable.Rows)
{
alTableName.Add(dataRow[0].tostring());
//...
}