How to Select already existing entries in a column without using mouse or having to check 'Filter' option: Pressing Alt key and down arrow at the same time, shows the list of previously keyed-in entries, in that column.
For exampleIn a particular column, suppose you are typing list of data : Names of Customers, and you want to check whether a particular name is previously Keyed in or not, then, without having to use the filter option and check the drop down values there , you can press Alt +↓ (down arrow) simultaneously, In the same cell, excel will show the list of all unique values already keyed in.