PostgreSQL basics & clauses.

• SQL:Structured query language
  It is programming language for storing and processing information in a relational database.

• PostgreSQL:PostgreSQL (often called Postgres) is a free, open-source database management system and one of the type of SQL that stores and manages data in tables. It's known for its reliability, flexibility, and performance and can handle large amounts of data.

• CLAUSE
  A clause in PostgreSQL is like a piece of a sentence in a SQL query. It helps tell the database what to do with the data. Think of it as giving step-by-step instructions.

Clauses are building blocks of SQL queries and help define operations such as filtering, sorting, grouping, and joining data.

-- FILTERING: Get employees older than 30
SELECT * FROM employees WHERE age > 30;

-- SORTING: Get employees sorted by salary (highest first)
SELECT * FROM employees ORDER BY salary DESC;

-- GROUPING: Count employees in each department
SELECT department, COUNT(*) FROM employees GROUP BY department;

-- JOINING: Get employees with their department names
SELECT employees.name, departments.name 
FROM employees 
JOIN departments ON employees.department_id = departments.id;