De Morgan's Law in SQL
Logic can quickly become convoluted when you start nesting NOT, AND, and OR in SQL.
De Morgan’s Law provides a way to simplify.
The Law
\[\neg (A \land B) = (\neg A) \lor (\neg B)\] \[\neg (A \lor B) = (\neg A) \land (\neg B)\]This gives us a way to rewrite negated conditions into something more readable in SQL.
Imagine you need to find users who are not from India or the USA.
A common approach:
SELECT * FROM users
WHERE NOT (country = 'India' OR country = 'USA');Using De Morgan’s Law, you can simplify:
SELECT * FROM users
WHERE country <> 'India' AND country <> 'USA';It is logically equivalent and simpler.