how can I draw database diagram using toad?
If you are using Toad for Oracle you can simply go into the Schema Browser and right-click on a table and choose Create ER Diagram. This will prompt you for how many levels of relationships you want to display in the diagram.
If you are working with PL/SQL you can go into Schema Browser and right-click on a package and choose Code Road Map and create an ER diagram for your PL/SQL code.
-Mark