Security, Transactions, and Views

1. Security, Transactions, and Views

2. About Security As is the case in most shared environments, the DBMS also must implement a security mechanism that allows the setting of permissions to data and actions pertaining to that data. This is required to ensure data security.

3. GRANT Command This “grants” a user or group of users permission to manipulate specified data in specified ways. GRANT {ALL | privilege_list}ON {table_name | view_name [(col_list)]}TO {PUBLIC | user_list}

4. REVOKE Command This “revokes” a granted permission issued by GRANT from a specified user. REVOKE {ALL | privilege_list}ON {table_name | view_name [(col_list)]}FROM {PUBLIC | user_list} Tip:1) You GRANT TO and REVOKE FROM.2) The most recently issued statement supercedes all others.

5. Views A view is representation of an existing table which corresponds to the SELECT statement that created it. The view can then be manipulated much like an actual table. A view is not a separate table or entity. It’s more like a mask of the actual table.

6. Uses of a VIEW • Hiding sensitive data from users • Preserving a previous table schema • Presenting data to users in a desired format. • Simplify a complex query

7. Creating a VIEW CREATE VIEW view_name [(col_name…)]ASSELECT _statement

8. Dropping a VIEW DROP VIEW view_name Only drops the view… not the table.

9. More about Views • The view displays like any table and the data you see is the actual data in the table(s). • A view is more for viewing rather than updating since an update could disqualify a record from the view. • Updates made to a view are made to the table(s) and any changes made to the table(s) are reflected in the view.

10. Naming View Columns • Column names are inherited from the underlying tables. • New names can be assigned • Columns must be renamed when using arithmetic expressions or when more than one column has the same name.

11. Transactions A transaction is a set of SQL statements that represent a unit of work or a procedural operation. A transaction is not complete unless all off its steps are followed through. This can be critical to maintaining data integrity such as when an account must be credited while debiting another.

12. Locking Since many users may be trying to access the same data simultaneously the DBMS has a locking mechanism which locks data which is in use. This provides a solution to concurrency problems which would arise if locking were not available.

13. Defining a Transaction • A transaction starts with the keyword BEGIN BEGINSQL statementSQL statementSQL statement

14. Finishing the Transaction • If the transaction goes successfully then the COMMIT command will commit the changes to the database. • However, if an error occurs the ROLLBACK command can be used to restore the database to its state prior to the transaction.