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Visual C#, SQL query from an existing DataTable?

Say if I populate a DataTable with a SQL command like this:
SQLCmd.Parameters.AddWithValue("#Date",DateTime.Today());
SQLCmd.CommandText = #"select ID, Name, Date from TestTable1 where Date=#Date";
SqlDataAdapter SQLAdapter = new SqlDataAdapter(SQLCmd);
DataTable dt = new DataTable();
SQLAdapter.Fill(dt);
Is it possible do a further query looking for something in another table which is also in dt?
For example, do something like
select ID
from TestTable2
where TestTable2.ID = dt["ID"];
Something like that... assuming both TestTable1 and TestTable2 have a column ID.
Thanks for helping!

You could use linkserver to get the data at a time or else below code may help you out. Get all the IDs with "," separated and passed it to second query.
string ids = String.Join(",", dt.AsEnumerable().Select(x => x.Field<int>("ID").ToString()).ToArray());
SQLCmd.Parameters.AddWithValue("#ID",ids);
SQLCmd.CommandText = #"select ID from TestTable2 where ID in ("+#ID+")";
SqlDataAdapter SQLAdapter = new SqlDataAdapter(SQLCmd);
DataTable dt2 = new DataTable();
SQLAdapter.Fill(dt2);

Just as an alternative option to think about, you could JOIN TestTable2 like:
SELECT t1.[ID]
,t1.[Name]
,t1.[DATE]
,t2.[ID]
FROM TestTable1 t1
INNER JOIN TestTable2 t2 ON t1.ID = t2.ID
WHERE t1.[DATE] = #Date

You can filter using DataView
DataView dv = new DataView(dt);
dv.RowFilter = "query"; // query example = "DATE = 'Your Date'"

mysql selecting with join to dataset and datatable in c#

I searched a lot but could not find the right solution.
Lets say ill select data like:
using(MySqlConnection connection = new MySqlConnection(MyConnectionString))
using(MySqlCommand cmd = connection.CreateCommand())
{
connection.Open();
cmd.CommandText = "SELECT a.Id, a.Foo, b.Bar FROM tableA a, tableB b where a.Id = b.Id";
MySqlDataAdapter da = new MySqlDataAdapter(cmd);
DataSet ds = new DataSet();
da.Fill(ds);
DataTable dt = ds.Tables[...]; //<== here is the problem
}
and I want to add this to a datatable,
How do I call the table in this case ?
Is it tableA ?
Does it matters how I name it ? (could I name it foobar as well???)

It is unclear what you are really asking for, but due to the length of comment and clarification, putting into an answer.
If you are trying to get multiple query results back from MySQL into a single "DataSet" (which can contain multiple tables), your query could contain multiple sql-statements and each would be returned into the dataset for you as different table results. For example, if you did something like...
using(MySqlConnection connection = new MySqlConnection(MyConnectionString))
using(MySqlCommand cmd = connection.CreateCommand())
{
connection.Open();
cmd.CommandText =
#"select * from TableA;
select * from TableB;
SELECT a.Id, a.Foo, b.Bar FROM tableA a, tableB b where a.Id = b.Id;";
MySqlDataAdapter da = new MySqlDataAdapter(cmd);
DataSet ds = new DataSet();
da.Fill(ds);
}
Your dataset would have 3 tables in it in direct correlation of the queries provided..
ds.Tables[0] = result of tableA all records.
ds.Tables[1] = result of tableB all records.
ds.Tables[2] = result of JOIN query tableA and tableB.
you could then refer to them locally however you need to...
ds.Tables[0].TableName = "anyLocalTableNameReference".
var t1Recs = ds.Tables[0].Rows.Count;
etc... or even create your own individual datatable variable name without having to explicitly reference the dataset and table array reference
DataTable myLocalTableA = ds.Tables[0];
DataTable myLocalTableB = ds.Tables[1];
DataTable myJoinResult = ds.Tables[2];
Hopefully this clarifies a bunch with the querying and referencing of multiple data results returned and how to then reference to the tables individually.

How can I get A1 cell from a 97/03 Excel document with OleDB?

I've got a Excel 97/03 document that has "blabla" in its A1 cell in sheet "Sheet1". I thought the following should be able to extract it:
string con = #"Provider=Microsoft.Jet.OLEDB.4.0;Data Source=Book1.xls;" + #"Extended Properties='Excel 8.0;HDR=Yes;'";
using (OleDbConnection connection = new OleDbConnection(con))
{
connection.Open();
OleDbDataAdapter da = new OleDbDataAdapter("Select * From [Sheet1$]", connection);
DataTable dt = new DataTable();
da.Fill(dt);
dynamic cellA1 = dt.Rows[0][0].ToString();
But cellA1 is empty (""). Anyone know how to fix this, I should be able to treat it as a database and get cells from it?

"HDR=Yes;" indicates that the first row contains columnnames, not data. "HDR=No;" indicates the opposite. maybe thats the issue.

The datatable is using the first row of data as its headers, to access the A1 cell simply use the name of the first column:
dynamic cellA1 = dt.Columns[0].ToString();

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());
//...
}

Using SqlDataAdapter to insert a row

I want to insert a row into the Database using SqlDataAdapter. I've 2 tables (Custormers & Orders) in CustomerOrders database and has more than thousand records. I want to create a GUI (TextBoxes) for adding new customer & orders into the Database to their respective tables.
How should I do it?
I guess the method that is usually followed is
dataAdapter = new SqlDataAdapter (sqlQuery, conn);
dataSet = new DataSet();
da.Fill(dataSet);
Now take the values from textboxes (or use DataBinding) to add a new row into the dataSet and call
da.Update(dataSet);
But the Question is Why should I fetch all other records into dataSet using da.Fill(dataSet ) in the first place? I just want to add a single new record.
For this purpose what I'm doing is, Creating the schema of the Database in the DataSet. like this:
DataSet customerOrders = new DataSet("CustomerOrders");
DataTable customers = customerOrders.Tables.Add("Customers");
DataTable orders = customerOrders.Tables.Add("Orders");
customers.Columns.Add("CustomerID", Type.GetType("System.Int32"));
customers.Columns.Add("FirstName", Type.GetType("System.String"));
customers.Columns.Add("LastName", Type.GetType("System.String"));
customers.Columns.Add("Phone", Type.GetType("System.String"));
customers.Columns.Add("Email", Type.GetType("System.String"));
orders.Columns.Add("CustomerID", Type.GetType("System.Int32"));
orders.Columns.Add("OrderID", Type.GetType("System.Int32"));
orders.Columns.Add("OrderAmount", Type.GetType("System.Double"));
orders.Columns.Add("OrderDate", Type.GetType("System.DateTime"));
customerOrders.Relations.Add("Cust_Order_Rel", customerOrders.Tables["Customers"].Columns["CustomerID"], customerOrders.Tables["Orders"].Columns["CustomerID"]);
I used DataBinding to bind these columns to respective text boxes.
Now I'm confused! What should I do next? How to use Insert command? Because I didn't give any dataAdapter.SelectCommand so dataAdapter.Update() wont work I guess. Please suggest a correct approach.

Set the select command with a "0 = 1" filter and use an SqlCommandBuilder so that the insert command is automatically generated for you.
var sqlQuery = "select * from Customers where 0 = 1";
dataAdapter = new SqlDataAdapter(sqlQuery, conn);
dataSet = new DataSet();
dataAdapter.Fill(dataSet);
var newRow = dataSet.Tables["Customers"].NewRow();
newRow["CustomerID"] = 55;
dataSet.Tables["Customers"].Rows.Add(newRow);
new SqlCommandBuilder(dataAdapter);
dataAdapter.Update(dataSet);

You can fill the dataSet with an empty set e.g.:
da = new SqlDataAdapter ("SELECT * FROM Customers WHERE id = -1", conn);
dataSet = new DataSet();
da.Fill(dataSet);
Then you add your rows and call update.
For this scenario though it would probably be better not to use SqlDataAdapter. Instead use the SqlCommand object directly for insertion. (Even better, use LINQ to SQL or any other ORM)

SqlConnection con = new SqlConnection("Data Source=(local);Initial Catalog=test;Integrated Security=True");
SqlDataAdapter da=new SqlDataAdapter("Insert Into Employee values("+textBox1.Text+",'"+textBox2.Text+"','"+textBox3.Text+"',"+textBox4.Text+")",con);
DataSet ds = new DataSet();
da.Fill(ds);
I have to do first time. You can try it . It works well.