SELECT
 GGG.AAA,
 GGG.OOO as "BBB",
 GGG.VVV as "CCC",
 RRR."TTN",
 RRR.TTC,
 RRR."TTV",
 RRR.TTK,
 RRR.OOO as "XXX",
 COUNT( QQQ.AAA ) as "WWW"
FROM
 GGG
LEFT JOIN 
 RRR ON
 GGG.AAA = RRR.AAA
LEFT JOIN
 QQQ ON
 (
   ( GGG.AAA = QQQ.AAA )
   AND
   (
     ( GGG.OOO = QQQ.ZZZ )
     OR
     (
       ( GGG.OOO = RRR.OOO ) AND
       ( QQQ.ZZZ IS NULL )
     )
   )
 )
GROUP BY
 QQQ.AAA,
 BBB

UNION

/* QUERY2 */
SELECT
 QQQ.AAA,
 CASE
   WHEN QQQ.ZZZ IS NULL THEN RRR.OOO
   ELSE QQQ.ZZZ
 END BBB,
 GGG.VVV as "CCC",
 RRR."TTN",
 RRR.TTC,
 RRR."TTV",
 RRR.TTK,
 RRR.OOO as "XXX",
 COUNT( QQQ.AAA ) as "WWW"
FROM
 QQQ
LEFT JOIN
 RRR ON
 QQQ.AAA = RRR.AAA
LEFT JOIN
 GGG ON
 (
   ( RRR.AAA = GGG.AAA )
   
   AND
   
   (
     ( GGG.OOO = QQQ.ZZZ )

     OR

     (
       ( GGG.OOO = RRR.OOO ) AND
       ( QQQ.ZZZ IS NULL )
     ) 
   )
 )
 
WHERE

 GGG.VVV IS NULL
 
GROUP BY

 QQQ.AAA,
 BBB