Scanning tables and indexes

- [Narrator] Let's turn out attention … to scanning tables and indexes. … One of the simplest operations … in an execution plan is a scan operation. … This is basically the process … of accessing each row in a table. … We can also scan indexes, … which, really, are a special kind of table. … Scanning is a linear operation, … moving from one row to the next, … and performing some operation, … like applying a filter to implement a WHERE clause. … Scanning is simple. … The database fetches data blocks … from persistent storage or cache, … applies a filter, join, or other operation on the row, … and then moves on to the next row. … The time it takes to finish the scan is based … on the number of rows in the table. … Now, I should say, it's not always that simple. … Data is not always stored in a row-based fashion. … Column-based storage is used in data warehouse … and other big data applications. … This can make filtering based on the value … of a single or small number of columns … quite efficient when working with large tables. …