SQL - case, count dan subselect

SELECT DISTINCT  
       (SELECT COUNT("SUBJEK"."PD04MATRIK")
                FROM "SUBJEK"
                WHERE "SUBJEK"."PD04KODMP" = "SENARAI"."PD02KODMP" AND
                      "SUBJEK"."PD04SETMP" = "SENARAI"."PD02SETMP" AND
                      "SUBJEK"."PD04SESI" = :gs_sesi AND
                      "SUBJEK"."PD04SEMESTER" = :gs_semester ) AS EKSTRAPELAJAR,
       (SELECT COUNT("SUBJEK"."PD04MATRIK")-30
                FROM "SUBJEK"
                WHERE "SUBJEK"."PD04KODMP" = "SENARAI"."PD02KODMP" AND
                      "SUBJEK"."PD04SETMP" = "SENARAI"."PD02SETMP" AND
                      "SUBJEK"."PD04SESI" = :gs_sesi AND
                      "SUBJEK"."PD04SEMESTER" = :gs_semester) AS KIRATOLAK30,
       (SELECT (COUNT("SUBJEK"."PD04MATRIK")-30)*2/60
                FROM "SUBJEK"
                WHERE  "SUBJEK"."PD04KODMP" = "SENARAI"."PD02KODMP"  AND
                       "SUBJEK"."PD04SETMP" = "SENARAI"."PD02SETMP"  AND
                       "SUBJEK"."PD04SESI" = :gs_sesi  AND
                       "SUBJEK"."PD04SEMESTER" = :gs_semester) AS KIRAMINIT,
        (CASE
                 WHEN (SELECT (COUNT("SUBJEK"."PD04MATRIK")- 30)*2/60
                FROM "SUBJEK"
                WHERE  "SUBJEK"."PD04KODMP" = "SENARAI"."PD02KODMP"
                                AND    "SUBJEK"."PD04SETMP" = "SENARAI"."PD02SETMP"
                                AND    "SUBJEK"."PD04SESI" = :gs_sesi
                                AND    "SUBJEK"."PD04SEMESTER" = :gs_semester) < 0 THEN 0.00
                 ELSE (SELECT (COUNT("SUBJEK"."PD04MATRIK")-30)*2/60
                FROM "SUBJEK"
                WHERE "SUBJEK"."PD04KODMP" = "SENARAI"."PD02KODMP"
                                AND  "SUBJEK"."PD04SETMP" = "SENARAI"."PD02SETMP"
                                AND  "SUBJEK"."PD04SESI" = :gs_sesi
                                AND  "SUBJEK"."PD04SEMESTER" = :gs_semester)
                END) AS KIRAMINIT_2,
       "BEBAN_PENGAJARAN"."NOSTAF",
       "BEBAN_PENGAJARAN"."KODMP",
       "BEBAN_PENGAJARAN"."SEKSYEN",
       "BEBAN_PENGAJARAN"."SESI",
       "BEBAN_PENGAJARAN"."SEM",
       "SENARAI"."PD02THPPGN",
       "SENARAI"."PD02K",
       "BEBAN_PENGAJARAN"."JUM_BEBAN",
       "BEBAN_PENGAJARAN"."KREDIT",
       "BEBAN_PENGAJARAN"."MP_BAYAR"
  FROM "PENSYARAH",
       "BEBAN_PENGAJARAN",
       "SENARAI"
 WHERE BEBAN_PENGAJARAN.nostaf (+) = PENSYARAH.pd02pensy AND
       BEBAN_PENGAJARAN.kodmp (+) = PENSYARAH.pd02kodmp AND
       BEBAN_PENGAJARAN.seksyen (+) = PENSYARAH.pd02setmp AND
       BEBAN_PENGAJARAN.sesi (+) = PENSYARAH.pd02sesi AND
       BEBAN_PENGAJARAN.sem (+) = PENSYARAH.pd02semester AND
       "PENSYARAH"."PD02KODMP" = "SENARAI"."PD02KODMP" AND
       "PENSYARAH"."PD02SESI" = "SENARAI"."PD02SESI" AND
       "PENSYARAH"."PD02SEMESTER" = "SENARAI"."PD02SEMESTER" AND
       "PENSYARAH"."PD02SETMP" = "SENARAI"."PD02SETMP" AND
       "PENSYARAH"."PD02PENSY" = :gs_nostaf AND
       "PENSYARAH"."PD02SESI" = :gs_sesi AND
       "PENSYARAH"."PD02SEMESTER" = :gs_semester

* output utama sebenarnya nak kira jumlah pelajar untuk seseorang pensyarah, bagi sesi tertentu, semester tertentu dan seksyen tertentu
*case kiraminit_2 nak jadikan nilai '-'ve kepada 0.00 dan setkan nilai yang telah dibuat pengiraan


--to be continued