SQL Performance Explained, hands-down https://sql-performance-explained.com/ https://sql-performance-explained.com/ Covers all the main DBMS, explained very si

SQL Performance Explained, hands-down https://sql-performance-explained.com/ https://sql-performance-explained.com/ Covers all the main DBMS, explained very simply from the bottom up, maintained constantly and has been read and recommended by people for years and years.