Is it possible to use where clause in the LOOP AT...ENDLOOP. statement.

Is it possible to use where clause in the LOOP AT...ENDLOOP. statement?

The general practice seen is that first using a select statement, the resultset is chosen and then LOOPING at internal table the manipulated records in the resultset are displayed as a part of output as per the requirement.

If it is possible to use where clause in LOOP AT...ENDLOOP. statement, does it lead to any performance issue or is it absurd(not a usual practice).

I am a beginer in ABAP and want to get the some ideas crystal clear.