free barcode generator source code in vb.net REVOKE SELECT, UPDATE ON ORDERS FROM LARRY CASCADE in Software

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REVOKE SELECT, UPDATE ON ORDERS FROM LARRY CASCADE
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revokes not only Larry s privileges, but Bill s as well. The effect of the REVOKE statement thus cascades to all other users whose privileges have flowed from the original GRANT. Now, assume the same circumstances and this REVOKE statement:
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REVOKE SELECT, UPDATE ON ORDERS FROM LARRY RESTRICT
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In this case, the REVOKE fails. The RESTRICT option tells the DBMS not to execute the statement if it will affect any other privileges in the database. The resulting error calls the user s attention to the fact that there are (possibly unintentional) side-effects of
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the REVOKE statement and allows the user to reconsider the action. If the user wants to go ahead and revoke the privileges, the CASCADE option can be specified. The SQL2 version of the REVOKE statement also gives a user more explicit, separate control over privileges and the GRANT OPTION for those privileges. Suppose again that Larry has been granted privileges on the ORDERS table, with the GRANT OPTION for those privileges. The usual REVOKE statement for those privileges:
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REVOKE SELECT, UPDATE ON ORDERS FROM LARRY
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takes away both the privileges and the ability to grant those privileges to others. The SQL2 standard permits this version of the REVOKE statement:
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If the statement is successful, Larry will lose the ability to grant these privileges to other users, but he will not lose the privileges themselves. As before, the SQL2 standard requires the CASCADE or the RESTRICT option to specify how the DBMS should handle the statement if Larry has, in turn, granted the GRANT OPTION to other users.
Summary
The SQL language is used to specify the security restrictions for a SQL-based database: I The SQL security scheme is built around privileges (permitted actions) that can be granted on specific database objects (such as tables and views) to specific user-ids (users or groups of users). I Views also play a key role in SQL security because they can be used to restrict access to specific rows or specific columns of a table. I The GRANT statement is used to grant privileges; privileges that you grant to a user with the GRANT OPTION can in turn be granted by that user to others. I The REVOKE statement is used to revoke privileges previously granted with the GRANT statement.
DATABASE STRUCTURE
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The System Catalog
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SQL: The Complete Reference
database management system must keep track of a great deal of information about the structure of a database to perform its data management functions. In a relational database, this information is typically stored in the system catalog, a collection of system tables that the DBMS maintains for its own use. The information in the system catalog describes the tables, views, columns, privileges, and other structural features of the database. Although the DBMS maintains the system catalog primarily for its own internal purposes, the system tables or views based on them are usually accessible to database users as well, through standard SQL queries. A relational database is thus self-describing; using queries against the system tables, you can ask the database to describe its own structure. General-purpose database front-ends, such as query tools and report writers, use this self-describing feature to generate lists of tables and columns for user selection, simplifying database access. This chapter describes the system catalogs provided by several popular SQL-based DBMS products and the information that the catalogs contain. It also describes the system catalog capabilities specified by the ANSI/ISO SQL2 standard.
What Is the System Catalog
The system catalog is a collection of special tables in a database that are owned, created, and maintained by the DBMS itself. These system tables contain data that describes the structure of the database. The tables in the system catalog are automatically created when the database is created. They are usually gathered under a special system user-id with a name like SYSTEM, SYSIBM, MASTER, or DBA. The DBMS constantly refers to the data in the system catalog while processing SQL statements. For example, to process a two-table SELECT statement, the DBMS must: I Verify that the two named tables actually exist. I Ensure that the user has permission to access them. I Check whether the columns referenced in the query exist. I Resolve any unqualified column names to one of the tables. I Determine the data type of each column. By storing structural information in system tables, the DBMS can use its own access methods and logic to rapidly and efficiently retrieve the information it needs to perform these tasks. If the system tables were used only internally to the DBMS, they would be of little interest to database users. However, the DBMS generally makes the system tables available for user access as well. If the system tables themselves are not made available, the DBMS generally provides views based on the system tables that offer a set of user-retrievable catalog information. User queries against the system catalogs or views are almost always permitted by personal computer and workgroup class databases. These queries are also supported by mainframe and enterprise DBMS products, but
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