Oracle: Invalid identifier - oracle

Question

I am using the following query in oracle. However, it gives an error saying that "c.par" in line 5 is an invalid parameter. No idea why. The columns exist. I checked. I have been struggling with this for a long time. All I want to do is to merge one table into another and update it using oracle. Could someone please help?
MERGE INTO SPRENTHIERARCHIES
USING ( SELECT c.PARENTCATEGORYID AS par,
e.rootcategoryId AS root
FROM SPRENTCATEGORIES c,SPRENTHIERARCHIES e
WHERE e.root (+)= c.par
) SPRENTCATEGORIES
ON (SPRENTHIERARCHIES.rootcategoryId = SPRENTCATEGORIES.parentcategoryId)
WHEN MATCHED THEN
UPDATE SET e.root=c.par

Answer 1

The e and c aliases only exist within the query in the using clause. You're trying to refer to them in the update clause. You're also using a column alias from the using clause against the target table, which doesn't have that column (unless your tables have both rootcategoryId and root, and parentCategoryId and par).
So this:
UPDATE SET e.root=c.par
should be:
UPDATE SET SPRENTHIERARCHIES.rootcategoryId= SPRENTCATEGORIES.par
And in that using clause you're trying to use column aliases as the same level of query, so this:
WHERE e.root (+)= c.par
should be:
WHERE e.rootcategoryId (+)= c.PARENTCATEGORYID
Your on clause is wrong too, as that is not using the column alias:
ON (SPRENTHIERARCHIES.rootcategoryId = SPRENTCATEGORIES.par)
But I'd suggest you replace the old syntax in the using clause with proper join clauses:
MERGE INTO SPRENTHIERARCHIES
USING ( SELECT c.PARENTCATEGORYID AS par,
e.rootcategoryId AS root
FROM SPRENTCATEGORIES c
LEFT JOIN SPRENTHIERARCHIES e
ON e.rootcategoryId = c.PARENTCATEGORYID
) SPRENTCATEGORIES
ON (SPRENTHIERARCHIES.rootcategoryId = SPRENTCATEGORIES.par)
WHEN MATCHED THEN
UPDATE SET SPRENTHIERARCHIES.rootcategoryId= SPRENTCATEGORIES.par
You have a more fundamental problem though, as you're trying to update a joining column; this will get:
ORA-38104: Columns referenced in the ON Clause cannot be updated
As Gordon Linoff suggested you can use an update rather than a merge. Something like:
UPDATE SPRENTHIERARCHIES h
SET h.rootcategoryId = (
SELECT c.PARENTCATEGORYID
FROM SPRENTCATEGORIES c
WHERE c.PARENTCATEGORYID = h.rootCategoryID
)
WHERE EXISTS (
SELECT null
FROM SPRENTCATEGORIES c
WHERE c.PARENTCATEGORYID = h.rootCategoryID
)
The where exists clause is there in case there not be a matching record - which the outer join in your original query implies. But in this form it's even more obvious that you're going to update rootcategoryId to the same value, since you're selecting the parentCategoryID which is equal to it. So the update (or merge) seems to be pointless.