Codd's Twelve Rules - Rule 3 - Systematic treatment of NULL values

Codd's Twelve Rules - Rule 3 - Systematic treatment of NULL values

Rule 3	Systematic treatment of NULL values
Rule	NULL values (distinct from empty character string or a string of blank characters and distinct from zero or any other number) are supported in the fully relational RDBMS for representing missing information in a systematic way, independent of data type.
Description	This rule demands that we must be able to use a NULL placeholder irrespective of data type used. NULLs are distinct from an empty character string or any other number, and they are always to be considered as unknown values. This rule insists provisions for manipulating NULL values in all the possible ways.
Example	SELECT Emp_Salary FROM Employee WHERE EPhone IS NULL;           This query should return Emp_Salary if EPhone value is NULL/Not known.
Some DBMS that fulfills this property	Oracle, SQL Server, and MySQL supports NULL values to be handled. They provide mechanisms to handle NULL values like other values.

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Codd's Twelve Rules - Rule 7 - High level Insert, Update, and Delete

Codd's Twelve Rules - Rule 7 - High level Insert, Update, and Delete

Rule 7	High level Insert, Update, and Delete
Rule	The capability of handling a base relation or a derived relation as a single operand applies not only to the retrieval of data but also to the insertion, update, and deletion of data.
Description	This rule stresses the set-oriented nature of a relational database. It requires that rows be treated as sets in insert, delete, and update operations. The rule is designed to prohibit implementations that support only row-at-a-time, navigational modification of the database. The SQL language covers this via the INSERT, UPDATE, and DELETE statements.
Example	SQL Server,          MySQL, and Oracle support bulk insert, delete, and update.           INSERT INTO yourtable VALUES (1,2), (5,5), ...; - this can be used to insert multiple rows at a time in MySQL.
Some DBMS that fulfills this property	SQL Server,          MySQL, and Oracle

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Codd's Twelve Rules - Rule 4 - Dynamic Online Catalog Based on the Relational Model

Codd's Twelve Rules - Rule 4 - Dynamic Online Catalog Based on the Relational Model

Rule 4	Dynamic Online Catalog Based on the Relational Model
Rule	The database description is represented at the logical level in the same way as ordinary data, so authorized users can apply the same relational language to its interrogation as they apply to regular data.
Description	This rule requires that a relational database be self-describing. In other words, the database must contain certain system tables whose columns describe the structure of the database itself, or alternatively, the database description is contained in user-accessible tables. In other words, this rule insists a data dictionary that stores meta data.
Example	INFORMATION_SCHEMA system views in SQL Server,   INFORMATION_SCHEMA  information database in MySQL, and Oracle Data dictionary resides in SYSTEM tablespace and can be accessed using the prefixes USER, ALL, or DBA.
Some DBMS that fulfills this property	SQL Server, MySQL, and Oracle.

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Codd's Twelve Rules - Rule 5 - Comprehensive Data Sublanguage Rule

Codd's Twelve Rules - Rule 5 - Comprehensive Data Sublanguage Rule

Rule 5	Comprehensive Data Sublanguage Rule
Rule	A relational system may support several languages and various modes of terminal use. However, there must be at least one relational language that has a linear syntax, can be used both interactively and within application programs, supports data definition operations (including view definitions), data manipulation operations (update as well as retrieval), security and integrity constraints, and transaction management operations (begin, commit, and rollback).
Description	This rule insist the existence of SQL like language to manipulate data. Manipulation should involve all the above said things (highlighted in blue color).
Example	Transact-SQL satisfies the manipulation in SQL Server, SQL satisfies the data manipulation in Oracle and MySQL support a subset of ANSI SQL.
Some DBMS that fulfills this property	T-SQL in SQL Server, SQL in Oracle, ANSI SQL in MySQL, SQL in IBM DB2

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