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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