sqldeveloper – How to return an empty value in a column?

                        Basically, the logic should be the following. AC back (airplanes) on which component RCF6709 is installed (case 1) or not installed (case 0). See:

1) Search for an active plane in AC_Master;
2) Considering that it must have 1 pn RCF6709 per aircraft, I pleaded to be able to count 1 (OK) or 0 (not installed);
3) I believe the error is in the line where I put "WHERE A.PN IN (" RCF6709 "), because today the query returns all that which is installed (case 1). But when I extract the bruno report, I identify that there are 5 acs (planes) on which this pn is not installed.

Can you help me, please?

SELECT B.AC,
A.PN,
COUNT (DISTINCT (A.AC)) AS "NUMBER OF CONTROLS",
B.AC_TYPE || & # 39; – & # 39; || B.AC_SERIES AS "TYPE / SERIES",
(CAS WHEN COUNT (DISTINCT (A.AC)) = 1 THEN 1 OTHER 0 END) "CHECK"

FROM ODB.PLANNING A
JOIN LEFT ODB.AC_MASTER B
ON A.AC = B.AC

O A.PN IN (& # 39; RCF6709 & # 39;)

AND B.AC_TYPE || & # 39; – & # 39; || B.AC_SERIES = & # 39; ATR72-600 & # 39;

AND B.STATUS = & # 39; ACTIVE & # 39;

GROUP BY B.AC,
B.AC_TYPE || & # 39; – & # 39; || B.AC_SERIES,
A.PN