Using subqueries in ABAP

Here i'm gonna show on performance of using the sub quereis in program instead of two select statements..

For EX: Using the two select statements ...

SELECT * FROM SPFLI

  INTO TABLE T_SPFLI

  WHERE CITYFROM = 'FRANKFURT'

    AND CITYTO = 'NEW YORK'.

SELECT * FROM SFLIGHT AS F

    INTO SFLIGHT_WA

    FOR ALL ENTRIES IN T_SPFLI

    WHERE SEATSOCC < F~SEATSMAX

      AND CARRID = T_SPFLI-CARRID

      AND CONNID = T_SPFLI-CONNID

      AND FLDATE BETWEEN '19990101' AND '19990331'.

ENDSELECT.

For EX: the above two select statements can be replaced by  the sub queries

SELECT * FROM SFLIGHT AS F INTO SFLIGHT_WA

    WHERE SEATSOCC < F~SEATSMAX

      AND EXISTS ( SELECT * FROM SPFLI

                     WHERE CARRID = F~CARRID

                       AND CONNID = F~CONNID

                       AND CITYFROM = 'FRANKFURT'

                       AND CITYTO = 'NEW YORK' )

      AND FLDATE BETWEEN '19990101' AND '19990331'.

ENDSELECT.

And performance wise also sub queries is far better.