In this sample I'll show you how to access a database schema programmatically. As you can see from figure 10-36, I created a Windows application with one text box, three buttons, and two list boxes. The Browser button lets you browse .mdb database on your machine. The GetTables button then reads the database tables and adds them to the first list box. The Get Table Schema button returns table columns and their properties of the selected table on list box.

Listing 10-11 shows the source code for this application. As you can see, the BrowseBtn_Click handler browsers Access database on the machine fills the selected database name to the text box, and sets dbName as the database name, which is a string type of variable defined as follows:

        }

The GetOleDbSchemaTable method of OleDbConnection returns a data table object containing database tables. As you can see from the GetTableBtn_Click handler in Listing 10-12, I set the dataset to the left list box with the DisplayMember property as TABLE_NAME. I set DesplayMember because I want to show only one column of the data table in the list box. 

GetSchemaBn_Click listed in Listing 10-13 is the event handler that returns the columns and their properties of a database table. You read the database table using SELECT * and use DataTable to get columns. The DataColumn class defines unique, column data type, column name, and so on.

It isn't hard to select unique rows from a database table using SELECT DISTINCT, but sometimes people get stuck on this. So, it's not a bad idea to talk about the procedure.

You can use the SELECT DISTINCT SQL statement to select distinct records from a database. This is useful when you want to return only one record corresponding to a criterion. Listing 10-14 returns distinct records from the Employees table ordered by the LastName.