DBMS

There are many databases like RDBMS, GRAPH DATABASE, etc…

Relation–>Table (One way to think about databases in contex of rdbms is think about Table).

Table: A set of rows and column

Column: Field/ Atribute(Most common terms)

Rows: Toupls/Records

Instance: Set of touple/rows along with the table structure. So, number of instance = number of touples/records/rows

Key: Minimum set of atributes/column to uniquely identify a touples/rows

Here Cust_Id is he Key which is uniquely identify the rows but the combinaion of Cust_Id  +  Cust_name is not is not a Key because we dont need both of them to uniquely identify the toples/row/record.

Lets take another exaple:

Cust_name + Cust_Address is the Key because separately Cust_name & Cust_Address can not able to uniquely identify the any records becase Cust_name may be duplicated or address may be duplicated but the combination of both willbe able to identify the unique record in the table.

Simple Key: The Key having one attribute is called as Simple Key

Compound Key: Key with multiple atributes is called as compound key. For ex. Cust_name + Cust_Address 

Candidate Key : Set of all unique key is called as Unique Key

{Customer_id, {Cust_name + Cust_Address }}

Primary Key: One of the Candidate Key that DB-Designer chooses to maintain the uniqueness.

Rule for Primary Key:

1: Can not be null for any tuples

2: Atmost one primary Key

3: Unique for each row/tuple