PostgreSQL WHERE Clause: A Beginner's Guide

The WHERE clause is one of the first SQL concepts you should learn. It allows you to filter rows and return only the records that satisfy a condition.

Basic WHERE Example

SELECT id, name, city
FROM customers
WHERE city = 'Delhi';

The query returns only customers whose city is Delhi.

Comparison Operators

You can use operators such as =, <>, >, <, >= and <=.

SELECT *
FROM products
WHERE price > 1000;

Using AND and OR

SELECT *
FROM employees
WHERE department = 'IT'
  AND salary > 50000;

AND requires both conditions to be true. OR allows either condition to match.

Using IN

SELECT *
FROM customers
WHERE city IN ('Delhi', 'Mumbai', 'Pune');

Using LIKE

SELECT *
FROM customers
WHERE name LIKE 'A%';

This finds names beginning with the letter A.

Handling NULL

NULL should be checked with IS NULL or IS NOT NULL rather than using the normal equality operator.

SELECT *
FROM employees
WHERE manager_id IS NULL;

Final Thoughts

A strong understanding of WHERE makes filtering, reporting and troubleshooting much easier in PostgreSQL and SQL in general.