Oracle “Cannot update to NULL”

Question

I have this query on Oracle 10g:

UPDATE "SCHEMA1"."CELLS_GLIST" 
SET ("GLIST_VALUE_ID", "USER_ID", "SESSION_ID") = (
    SELECT "GLIST_VALUE_ID", 1 AS "USER_ID", 123456 AS "SESSION_ID"
    FROM "SCHEMA1"."GLISTS_VALUES_UOR"
    WHERE ("UOR_ID"=3)
    AND ("GLIST_ID"=67)
    AND ("GLIST_VALUE_DESC" = (
        SELECT "GLIST_VALUE_DESC"
        FROM "BMAN_TP1"."GLISTS_VALUES_UOR"
        WHERE ("UOR_ID"=3)
        AND ("GLIST_VALUE_ID"="CELLS_GLIST"."GLIST_VALUE_ID")
    ))
)
WHERE EXISTS (......)

It keeps saying ORA-01407: cannot update ("SCHEMA1"."CELLS_GLIST"."SESSION_ID") to NULL

"SESSION_ID" is obviously Not Nullable, but I'm actually passing a value to that field, so I do not understand the problem.

Answer 1

I found this query also to work:

UPDATE "BMAN_TP1"."CELLS_GLIST" 
SET "GLIST_VALUE_ID" = (
    SELECT "GLIST_VALUE_ID"
    FROM "BMAN_TP1"."GLISTS_VALUES_UOR"
    WHERE ("UOR_ID"=3)
    AND ("GLIST_ID"=67)
    AND ("GLIST_VALUE_DESC" = (
        SELECT "GLIST_VALUE_DESC"
        FROM "BMAN_TP1"."GLISTS_VALUES_UOR"
        WHERE ("UOR_ID"=3)
        AND ("GLIST_VALUE_ID"="CELLS_GLIST"."GLIST_VALUE_ID")
        ))
    ),
    "SESSION_ID" = 123456,
    "USER_ID" = 1
WHERE EXISTS (......)

But, it performs really really fast... I doubt I'm missing something...

Answer 2

From your comments, I read that you seem to want to write a default record to your target table, in case the subquery doesn't return any records. So the correct way to phrase your query would be using a MERGE statement as such:

MERGE INTO "SCHEMA1"."CELLS_GLIST" dst
USING (
  -- rephrase your subquery here. This is your "merge data source". The number
  -- of records returned in this subquery will correspond to the number of
  -- affected records in dst
) src
ON (
  -- the missing exists condition here. Everytime this condition matches a record
  -- between dst and src, an UPDATE is performed. Otherwise, an INSERT is
  -- performed
)
WHEN MATCHED THEN UPDATE 
  SET dst."GLIST_VALUE_ID" = src."GLIST_VALUE_ID"
WHEN NOT MATCHED THEN INSERT ("GLIST_VALUE_ID", "USER_ID", "SESSION_ID")
  VALUES (NULL, 1, 123456);

This is just to give you an idea. I'm not quite sure what you're trying to achieve in detail, so I omitted the subqueries and conditions