You can make selections in a table by clicking or drawing in the dimension columns.
Measure values cannot be selected. When you make a selection, it is always the dimension values that you select. You can only make selections in one column at a time.
Table with three selected fields in the dimension Customer.
To deselect a row, click it. To confirm a selection, click 
or click outside the visualization. You can also press Enter. To cancel, click 
or press Esc. If you confirm, the selection is reflected in all visualizations associated with the table.
You cannot select dimension values that are null. Null values in a table are presented as dashes (-). Rows without valid dimension values will not be included in the selection.