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DataTable expressions referencing to two different tables

I have two hidden Datatables, one of which gets its data from a database, and the other from a static .csv file. I want to create a DataGridView with columns that has custom datatable expressions (just like a spreadsheet).
My question is: how do I formulate expressions in the datagridview to search for data in the other two tables?
Example: Table B has references for each product, a static unique id. Table A also have a reference to each product but also includes status for that product.
In the DataGridView I have three columns (ID, PRODUCT, STATUS). How can I write the expressions to fetch data from the other tables?
This is just how I think this can be solved, if you have another idea please let me know.
Thank you!

using Merge two tables
1- convert table1 to dataTable dtOne.
2- convert csv data to dataTable dtTwo.
3- dtAll = new Datatable();
dtAll = dtOne.Copy();
dtAll.Merge(dtTwo);
dataGridView.DataSource=dtAll;

DataTable Sorting Then Assign Sorted Table Back To Original Table

I have a dataset that has a table called detail I want to sort. I know using a dataview I can sort the table with the following code..
Dim dvParsedDataset As New DataView(parsedDataset.Tables("Detail"))
dvParsedDataset.Sort = AuthorizatonConstants.Auth_ID
I want to not only sort the table but assign it back to the original table in this case parsedDataset.Tables("Detail") but when assigning the sorted view back I get a read only error
parsedDataset.Tables("Detail") = dvParsedDataset.ToTable 'READ ONLY ERROR
How do I sort the table and also override the original table with the sorted table?

You could remove the previous DataTable from the DataSet and the add the new table
DataTable detailCopy = dvParsedDataset.ToTable("Detail")
parsedDataset.Tables.Remove("Detail")
parsedDataset.Tables.Add(detailCopy)

add tables dynamically based on database schema

I have a DataSet to which I need to add tables dynamically at runtime, but these tables need to reflect the existing database structures. Is there a way to pull the schema (not data) of a specific table into a DataSet at runtime.
So, for instance, I might have an Account table (along with hundreds of others) in a database. I need to create an Account table in the DataSet at runtime (based on various actions of the end users) but there are too many to manually code this for each table.

You didn't specify wich database engine you were working on, so the best generic method to do what you want to do would be to use IDataReader's GetSchemaTable method.
More info on how to do this here.

If you run a SQL query that returns a datatable, it will have the structure of the table. Thus,
select * from SourceTable where 1 = 2;
Which returns no rows, but all the columns. DataSet fill, etc. Done.

You can programatically modify and examine your data schema and data. You can add Columns programatically to the DataSet: http://msdn.microsoft.com/en-us/library/hfx3s9wd.aspx
DataTable workTable = new DataTable("Customers");
DataColumn workCol = workTable.Columns.Add("CustID", typeof(Int32));
workCol.AllowDBNull = false;
workCol.Unique = true;
workTable.Columns.Add("CustLName", typeof(String));
workTable.Columns.Add("CustFName", typeof(String));
workTable.Columns.Add("Purchases", typeof(Double));
You can create new tables also into the DataSet. You can examine and traverse the schema of what you have: look at the Tables property of DataSet, it contains your DataTables (DataTableCollection). The DataTables contain Columns property. Knowing that it's straight forward.

load a datatable to an existing table in dataset

how can in load a DataTable to an existing table in my DataSet. something like this:
DataTable my_table = new DataTable("sale_info");
**add some row to my_table **
myDataSet.Tables.Add(my_table);
i have a table named sale_info in myDataset too and myDataSet.Tables.Add(my_table); is trying to add new one. actually i want update my table with new data from another table.

You can call myDataSet.Tables["sale_info"].Merge(my_table).
However, you should simply add the rows directly to the existing table rather than creating a new table.

How to make relation between tables which are in same dataset?

I have one dataset in which there are
40 tables. Now I want to make a relation
between these tables and show
important data in grid. How do i do this?

If you're creating a typed dataset, it's easiest to create the relations in Visual Studio's dataset designer. Just right-click on the table in the designer, select Add->Relation, and specify the relation.
If you need to specify the relation in code, you can do it like this:
dataSet.Relations.Add(dataSet.Tables["Customers"].Columns["customerId"],
dataSet.Tables["Orders"].Columns["customerId"]);
Read all about it in MSDN here.

That is a large number of DataTables to have in a DataSet.
The first thing I would consider would be to reduce the number of DataTables (and eliminate the need for Relations) by populating the DataTables with queries that JOIN the database tables. For example, instead of having one DataTable for Product Category and another for Product Detail, it might be possible to combine the data for both database tables into one DataTable. Similarly, for Customer, Customer Address and Customer Phone, retrieve all of the data in one DataTable by using one query that does a JOIN on all three database tables.
Once you have minimized the number of DataTables in the DataSet, you can add Relations between DataTables if they have matching columns (even if the columns have different names). For example, there might be an Orders DataTable with a CustomerID column that matches the ID column in the Customers DataTable.
Here is the code to add a Relation to the DataSet for that situation. Assume that we have a DataSet dst containing two DataTables Customers and Orders.
DataColumn customerColumn, orderColumn;
customerColumn = dst.Tables["Customers"].Columns["ID"];
orderColumn = dst.Tables["Orders"].Columns["CustomerID"];
DataRelation dr = new DataRelation("CustomerOrders", customerColumn, orderColumn);
dst.Relations.Add(dr);

ds.Relations.Add("Products_Category",
ds.Tables("Categories").Columns("CategoryID"),
ds.Tables("Products").Columns("CategoryID"));

Did you try something like:
ds.Relations.Add("Products_Category",
ds.Tables("Categories").Columns("CategoryID"),
ds.Tables("Products").Columns("CategoryID"));

private void CreateRelation()
{
// Get the DataColumn objects from two DataTable objects
// in a DataSet. Code to get the DataSet not shown here.
DataColumn parentColumn =
DataSet1.Tables["Customers"].Columns["CustID"];
DataColumn childColumn =
DataSet1.Tables["Orders"].Columns["CustID"];
// Create DataRelation.
DataRelation relCustOrder;
relCustOrder = new DataRelation("CustomersOrders",
parentColumn, childColumn);
// Add the relation to the DataSet.
DataSet1.Relations.Add(relCustOrder);
}