Thursday, February 19, 2015

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

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

Rule 2
Guaranteed Access 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.
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.
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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