Codd's Twelve Rules - Rule 2 - Guaranteed Access Rule

Codd's Twelve Rules - Rule 2 - Guaranteed Access Rule

Rule 2	Guaranteed Access Rule
Rule	Each and every datum (atomic value) is guaranteed to be logically accessible by resorting to a combination of table name, primary key value, and column name.
Description	We must be able to access every single piece of information from the tables in some way. The combination “Table name + Primary key + Column name” must let us find the information what we need. In the case of multiple records in the result, the combination of “Table name + Column name” or the “Table name + * “ would find what we need.
Example	SELECT Emp_Salary FROM Employee WHERE ENo = ‘101’;           where, Employee is table name, Emp_Salary is required field, and ENo is the primary key.
Some DBMS that fulfills this property	SQL in Oracle, Transact SQL in SQL Server, and SQL in MySQL supports primary keys, and are able to access the data as said above.

 

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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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