Написать странный запрос с update

 WITH a
         AS ( SELECT DISTINCT UNNEST(ARRAY['777', NULL]) "Ключ",
         UNNEST(ARRAY['111', '222']) "Знач"
         )
 UPDATE "Документы"
 SET "Название" = "Название" || '_' || a."Знач"
 FROM a
 WHERE "Id" IS NOT DISTINCT FROM  a."Ключ"
returning *

WITH a
         AS ( SELECT DISTINCT UNNEST(ARRAY['777', NULL]) "Ключ",
         UNNEST(ARRAY['333', '444']) "Знач"
         )
 UPDATE "Документы"
 SET "Название" = "Название" || '_' || a."Знач"
 FROM a
 WHERE
   EXISTS (
    SELECT TRUE
    FROM a
    WHERE "Id" = a."Ключ" AND "Id" IS NOT NULL AND a."Ключ" IS NOT NULL  
    UNION
     SELECT TRUE
    FROM a
    WHERE "Id" IS NULL AND a."Ключ" IS NULL
   )
returning *

WITH a
         AS ( SELECT DISTINCT UNNEST(ARRAY['777', NULL]) "Ключ",
         UNNEST(ARRAY['333', '444']) "Знач"
         ),
 qUpdNull AS (
    UPDATE "Документы"
    SET "Название" = "Название" || '_' || a."Знач"
    FROM a
    WHERE 
      a."Ключ" IS NULL AND "Id" IS NULL
    returning *
 ),  
 qUpdNotNull AS (
    UPDATE "Документы"
    SET "Название" = "Название" || '_' || a."Знач"
    FROM a
    WHERE 
      a."Ключ" IS NOT NULL AND "Id" = a."Ключ"
    returning *
 )
 
 SELECT * FROM qUpdNull
 UNION ALL
 SELECT * FROM qUpdNotNull