Important Concepts of Database: Keys, Joins, Query Optimization and Normalization

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Keys in Databases: SQL vs. NoSQL

Keys are fundamental elements in databases, acting as unique identifiers or references to ensure data integrity and efficient retrieval. Here’s a breakdown of key types in both SQL and NoSQL databases:

SQL Databases:

1. Primary Key (PK):

• Definition: A unique identifier for each row in a table. There can only be one primary key per table, and it cannot contain null values.

Example: Table: Customer (customer_id (PK), name, email)

customer_id uniquely identifies each customer record.

2. Candidate Key:

• Definition: Any set of attributes (columns) that can uniquely identify a row in a table. A table can have multiple candidate keys, but only one is chosen as the primary key.

Example: Table: Order (order_id (PK), customer_id, order_date)

Both order_id and customer_id (alone) can uniquely identify an order, but order_id is chosen as the primary key for efficiency.

3. Foreign Key (FK):

• Definition: A column (or set of columns) in one table that references the primary key of…