Sequential Table Scan

Each row of a table is stored as a record in a file. A data file contains the rows from one table. The most basic access method is to perform a sequential scan of a file where the table's rows are retrieved by sequentially reading through the file. Thus, the cost (measured in logical disk accesses) to perform a sequential scan of a table is equal to the number of pages in the file:

Escan = Cost of sequential file scan = P

A sequential file scan is used in queries where the WHERE clause contains no optimizable conditional expressions that reference foreign key, primary key, or indexed columns.