Update with row_number() not working, why? - sql

Question

I have the following table:
CREATE TABLE t_overview
(
obj_uid uuid,
obj_parent_uid uuid,
obj_no integer,
obj_text text,
obj_path text,
isdir integer,
intid bigint,
intparentid bigint
)
I want to move from uuid to bigint and created the new columns intid and intparentid. I need a unique integer (obj_uid is the primary key) for intid, so I just wanted to update with row_number() over (order by ...).
Did not seem to work. So I tried to write the results into a temp table, and update via join. But I got 1 for every intid.
But when I select from the join where I do the update, I get 1, 2, 3, 4, 5, 6 etc. What am I missing?
DROP TABLE IF EXISTS mytable;
CREATE TEMP TABLE mytable AS
WITH CTE AS
(
SELECT obj_uid, obj_parent_uid, obj_no
, obj_text, obj_path, isdir
, intid as cteIntId
, intparentid as cteParentId
, row_number() over (order by obj_uid) as rn
FROM T_Overview
)
SELECT * FROM CTE;
UPDATE T_Overview SET intid = mytable.rn
FROM T_Overview AS bt
INNER JOIN mytable
ON mytable.obj_uid = bt.obj_uid
-- UPDATE T_Overview SET intid = CTE.rn FROM CTE;
-- UPDATE T_Overview SET intparentid = CTE.intid FROM CTE;

Answer 1

#Frank already provided an explanation for your error.
But you don't need the temporary table at all:
BEGIN;
LOCK T_Overview; -- if there is concurrent write access
WITH cte AS (
SELECT obj_uid, obj_parent_uid
, row_number() OVER (ORDER BY obj_uid) AS intid
FROM T_Overview
)
UPDATE T_Overview t
SET intid = upd.intid
, intparentid = upd.intparentid
FROM (
SELECT t1.*, t2.intid AS intparentid
FROM cte t1
LEFT JOIN cte t2 ON t2.obj_uid = t1.obj_parent_uid
) upd
WHERE t.obj_uid = upd.obj_uid;
COMMIT;
The transaction wrapper and the explicit lock are only needed if there can be concurrent write access. (Even more so with a temp table, where you have a much bigger time slot in between.)
Assuming referential integrity - a FK constraint from T_Overview.obj_parent_uid to T_Overview.obj_uid. NULL values in obj_parent_uid are translated to NULL in intparentid.

Answer 2

Your update is wrong, there is no relation between T_Overview and (T_Overview + mytable).
This one should work:
UPDATE T_Overview SET intid = mytable.rn
FROM mytable
WHERE mytable.obj_uid = T_Overview.obj_uid;
Offtopic: Your CTE doesn't make much sense, a plain SELECT would give you the same results.