What is an index scan in SQL?

What is the difference between table scan and index scan?

Table scan means iterate over all table rows. Index scan means iterate over all index items, when item index meets search condition, table row is retrived through index. Usualy index scan is less expensive than a table scan because index is more flat than a table.

Is index scan better than table scan?

3) index scan is faster than a table scan because they look at sorted data and query optimizers know when to stop and look for another range. 4) index seek is the fastest way to retrieve data and it comes into the picture when your search criterion is very specific.

What is the difference between index scan and index seek?

Index scan means it retrieves all the rows from the table and index seek means it retrieves selective rows from the table.

What is index only scan?

The Index-Only Scan is an index scan without subsequent table access—hence, accessing the index only. All recent versions of Oracle, SQL Server and MySQL support index-only scans. The PostgreSQL database supports index-only scans since release 9.2.