SQL Performance: Understanding Index Seek vs. Index Scan SQL Performance: Understanding Index Seek vs. Index Scan Mastering "SQL query optimization" starts with understanding how the database engine retrieves data. The difference between an "Index Seek" and an "Index Scan" is critical to performance. For anyone involved in "coding SQL", optimizing performance often boils down to ensuring your queries trigger the most efficient data retrieval operations possible. When the SQL query optimizer processes a statement, it attempts to find the data requested in the fastest way. The two primary methods it uses to read data stored in a table's index structure (usually a "B-tree") are the "Index Seek" and the "Index Scan". Understanding the difference between these two operations—and how to make your queries favor the "Index Seek"...