What is the difference between PostgreSQL and MySQL?

PostgreSQL is a fully ACID-compliant, object-relational database with stronger standards compliance, more advanced SQL features, better support for complex queries, and richer data types (arrays, JSON, hstore, custom types). MySQL is simpler, historically faster for read-heavy workloads with MyISAM, and more widely deployed in LAMP stacks. Key differences: PostgreSQL supports partial indexes, expression indexes, and advanced join algorithms; it treats NULL consistently per SQL standard; it has no implicit data type coercions that silently truncate data. MySQL has a larger market share in legacy web apps. PostgreSQL is generally preferred for data integrity, analytics, and applications requiring complex queries or custom extensions.