![]() Let us look at an example of a table where the Emp Id is the Primary Key. If a foreign key refers to the primary key, then no value in this primary key column can be altered or modified.Any two rows in the table cannot have identical values for that column.The Primary Key field cannot be left NULL the Primary Key column must hold a value.We have a few rules for choosing a key as the Primary Key. There can be no duplicates in a Primary Key, meaning that there can be no two same values in the table. These keys help us distinctly identify any Employee row in the table.Ī primary Key is a column or a combination of columns in a relationship that helps us uniquely identify a row in that table. Let us look at an example of a table where the Emp Id, Mobile No, and Email are the Candidate keys. A Candidate Key must uniquely identify each row in the table.A Candidate Key cannot comprise null values.A Candidate Key can have various attributes.A Candidate Key should comprise distinctive values.There are a few rules that we need to follow regarding the selection of a Candidate Key. All tables are required to have one candidate key at least. We carefully choose the Primary Key after considering the given Candidate keys. We refer to a Super Key as a Candidate Key if it has no duplicate attributes. ![]() ![]() ![]() Let us look at an example where the EmpId and the Mobile number can be considered Super Keys. A Super key can have extra attributes that are redundant for distinct identification. A super key is either a single key or a set of keys that help identify distinct rows in a particular table. ![]()
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