TABLE SCAN 
TABLE SCAN is a search strategy of the SQL optimizer.
When Can the System Use This Strategy?
The database system uses the sequential search in the following cases:
No search conditions have been specified.
Neither the key columns nor the indexed columns are included in the search condition.
The available non-sequential search strategies would be more costly than the sequential search.
How Does the System Access the Data?
The database system sequentially searches through the entire table.