1/3/2024 0 Comments Super key in dbms![]() ![]() The candidate key helps in determining the prime and non-prime attributes of a table and ensures the integrity of the data by preventing duplicate data. Candidate keys are a subset of the super key superset. ![]() From this set of candidate keys, a primary key can be chosen, and doing this can prove difficult. They are single column in that they are not made by combining multiple columns. In other words, it is any set of columns that have a unique combination of values in each row, with the additional constraint that removing any column would possibly produce duplicate rows. Key’s attributes can contain NULL values.Ī relation, number of super keys are more than number of candidate keys.Ī candidate key, or simply a key, of a relational database is a minimal superkey. Super keys combined together creates the criteria to select the candidate Keys. Key is an attribute (or set of attributes) that is used to uniquely identify Unique for all possible sets of tuples in a table at all times. Super key is any set of attributes for which the values are guaranteed to be Super key is any combination of columns that uniquely identifies a row in a ![]() However, to ensure absolute uniqueness, a composite candidate key may be formed by combining customer ID with SSN. Therefore, the superkey may be reduced to just one field, customer ID, which is the candidate key. It can be assumed that the customer ID is unique to each customer. However, this process may be further reduced. As an example, a table used to store customer master details could contain columns such as:Ī certain set of columns may be extracted and guaranteed unique to each customer. ![]()
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