Sql keys and their types

 Sql Keys and their types

Introduction :

Sql keys is the key to your success in analytics! 

Data is growing at an exponential rate and so is the demand for professionals who are well verse3d with the databases. 

Organizations all over the world are looking for data scientists and analysts who can draw meaningful insights from the vast amounts of data. And one of the most important languages for handling databases is SQL. That is why those professionals with a background in SQL have an edge over their peers when it comes to working with databases. 

Table of Contents :

1.What are keys in DBMS 

2. Super key 

3.Candidate key 

4. Primary key 

 5 Alternate or Secondary key

 6.Foreign key

 7.Composite key 

 What are keys in DBMS  Database are used to store massive amounts of information which is stored across multiple tables. Each table might be running into thousands of rows. Needless to say, there will be many duplicate rows with redundant information. How do we deal with that? How do we manage records so that we are storing only unique data? And, how do we relate the multiple tables that are present in the database? 

 

 SQL keys are the answer to all these queries. 

An SQL key is either a single column (or attribute) or a group of columns that can uniquely identify rows (or tuples) in a table. 

 Super Key 

Super key is a single key or a group of multiple keys that can uniquely identify tuples in a table. Super key can contain multiple attributes that might not be able to independently identify tuples in a table, but when grouped with certain keys, they can identify tuples uniquely. 

 

Candidate key :

Candidate key is a single key or a group of multiple keys that uniquely identify rows in a table. A candidate key is a subset of super keys and is devoid of any unnecessary attributes that are not important for uniquely identifying tuples. 

 

Primary key 

 Primary key is the candidate key selected by the database administrator to uniquely identify tuples in table. Out of all the candidate keys that can be possible for a table, there can be only one key that will be used to retrieve unique tuples from the table. This candidate key is called the primary key. 

 

Alternate or Secondary key  

 There can be only one primary key for a table. Therefore all the remaining candidate keys are known as Alternate or Secondary keys. They can also uniquely identify tuples in a table, but the database administrator chose a different key as the primary key. 

 

Foreign key 

 Foreign key is an attribute which is a primary key in its parent table, but is included as an attribute in another host table. A foreign key generates a relationship between the parent table and the host table. For example, in addition to the Employee table containing the personal details of the employees, we might have another table department containing information related to the department of the employee. 

 

Composite key :

A composite key is a candidate key or primary key that consists of more than one attribute. Sometimes it is possible that no single attribute will have the property to uniquely identify tuples in a table.  In such cases, we can use a group of attributes to guarantee uniqueness. Combining these attributes will uniquely identify tuples in the table.