By using line_exists you can check if a line exists or not exists, but it is not possible to use other comparison operators. A workaround can be REDUCE in that case.
In the following snippet, we want to check if there is a flight that costs more than $1000,
SELECT * FROM sflight INTO TABLE @DATA(flights).
* Check if flight with price > 1000 exist
IF REDUCE abap_bool( INIT price_gt_1000 = abap_false
FOR line IN flights WHERE ( price > 1000 )
NEXT price_gt_1000 = abap_true ) EQ abap_true.
" flight with price > 1000 exists
ENDIF.