MySQL UNION Optimization

MySQL UNION Optimization is a SQL statement in the MySQL Specific category. MySQL UNION vs UNION ALL performance. UNION removes duplicates (filesort overhead). UNION ALL is much faster. The syntax is SELECT ... UNION ALL SELECT ...; -- ALL avoids dedup overhead.. It returns union optimization. A typical example: -- SLOW: UNION with implicit DISTINCT SELECT name FROM employees UNION SELECT name FROM contractors; -- MySQL must sort and compare all rows to remove duplicates -- FAST: UNION ALL (no dedup) SELECT name FROM employees UNION ALL SELECT name FROM contractors; -- Simply concatenates results -- When to use UNION: -- Only when you truly need distinct results -- For large result sets, consider: -- 1. UNION ALL +… A close relative is AUTO_INCREMENT, which mySQL auto-generates sequential integer values for this column. Commonly used with PRIMARY KEY. A close relative is ENGINE, which specifies the MySQL storage engine. InnoDB (default) supports transactions and foreign keys. MyISAM is faster for read-heavy.