Master Coding Skills &
System Design.

Learn indexes, EXPLAIN, when to add them, and why over-indexing slows writes.

Learn scalar subqueries, IN, NOT IN, EXISTS, correlated subqueries, and derived tables.

PHP performance — OpCache, fixing N+1 queries, APCu caching, and profiling with Xdebug.

Learn SQL injection, XSS, CSRF, and secure file uploads — the top PHP security threats and their defences.

Learn validation vs sanitization, filter_var, custom rules, and a reusable Validator class.

Learn PHP magic methods — __construct, __destruct, __get, __set, __toString, __invoke.

Learn static methods, static properties, utility classes, and the Singleton pattern.

Learn abstract classes vs interfaces with real-world examples and guidelines.

Understand PHP closures, use() capture, arrow functions, and uses with array functions.