Question

Given Codd's Rule 4:

Rule 4: Dynamic online catalog based on the relational model: The database description is represented at the logical level in the same way as ordinary data, so that authorized users can apply the same relational language to its interrogation as they apply to the regular data.

In three sentences, explain what this means. Give two example queries from MySQL that show how MySQL realizes the concepts

Answer 1

Meaning of the rule :

This rule simply means that Description of actual database should be similarly represented as we represent ordinary data( by tables, columns, views etc). you must be able to inquire about a database's meta-data using the same language that you use to inquire about the actual data. What tables are available? What columns do they contain? Such questions can be answered.

Database dictionary(catalog) is called the Catalog. Dynamic nature of Database is called dynamic online catalog. Thsi rule simply says that Management of dynamic database should be in threlational model. The structure description of the complete Database and it must be stored online. The Catalog must be governed by same rules as rest of the database. The same query language should be used on catalog as used to query database.

Give two example queries from MySQL that show how MySQL realizes the concepts:

MySQL does have system tables in a special database called "mysql", that contain access privilege information and
are used to authenticate users and determine what tables, databases, and columns they have privileges on and what type of privileges they have.
You can find more information here. https://dev.mysql.com/doc/refman/5.7/en/system-schema.html

Note : You must be logged in as root inorder to execute the below statement.

Get the current Timezone used by MySQL database

SELECT @@GLOBAL.time_zone, @@SESSION.time_zone;

Display the current structure of the log tables

SHOW CREATE TABLE mysql.general_log;