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Aug 30, 2024 · In DBMS, there are different types of keys available that are used for various purposes. Foreign Key is a column that refers to the primary key/unique key of another table. So it demonstrates the relationship between tables and acts as the cross reference among them. Foreign KeyForeign keys are a set of constraints in DBMS that establish relationsh
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- Primary key. It is the first key used to identify one and only one instance of an entity uniquely. An entity can contain multiple keys, as we saw in the PERSON table.
- Candidate key. A candidate key is an attribute or set of attributes that can uniquely identify a tuple. Except for the primary key, the remaining attributes are considered a candidate key.
- Super Key. Super key is an attribute set that can uniquely identify a tuple. A super key is a superset of a candidate key. For example: In the above EMPLOYEE table, for(EMPLOEE_ID, EMPLOYEE_NAME), the name of two employees can be the same, but their EMPLYEE_ID can't be the same.
- Foreign key. Foreign keys are the column of the table used to point to the primary key of another table. Every employee works in a specific department in a company, and employee and department are two different entities.
Jun 28, 2024 · Composite Key. Surrogate Key. Let’s look at each of the keys in DBMS with example: Super Key – A super key is a group of single or multiple keys which identifies rows in a table. Primary Key – is a column or group of columns in a table that uniquely identify every row in that table. Candidate Key – is a set of attributes that uniquely ...
Sep 26, 2022 · It can be a natural key, surrogate key, or a composite key. Using our earlier examples, these would be candidate keys for a “customer” table: Social Security Number. Customer ID. First Name, Last Name, Date of Birth. These keys are all candidate keys, as they are an option or candidate to be the primary key.
- Super Key. Everything we learned above is nothing but a super key. A super key is a set of all the keys (with single or multiple attributes) which can uniquely identify the records of the table.
- Candidate key. From all the super keys available, the candidate key is the one whose proper subset is not a super key. Don’t get it? Let’s see it with an example.
- Primary key. We learned to find candidate keys from a set of super keys. Now, the primary key is nothing but a candidate key which has given the right to be called the primary key.
- Alternate key. We learned the primary key is nothing but a candidate key given primary key rights. But what do we call all other candidate keys? Yes, you’re right.
The database key is an attribute or a group of attribute that can uniquely identify each record in a table . The keys are an important feature of a relational table. In relational database model , the logical structure of the database is represented by the number of interrelated tables. The DBMS access the data field in the table with reference ...
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Jun 27, 2022 · A single DBMS key can quickly identify the specific row of interest. Additionally, DBMS keys can identify multiple rows and reveal relationships between data tables. Some of the eight DBMS keys discussed in this article use a single identifier for finding data, while others may use multiple attributes together as the key. Types of keys in a DBMS
