PostgreSQL: duplicate key value violates unique constraint on UPDATE command - postgresql

Question

When doing an UPDATE query, we got the following error message:
ERROR: duplicate key value violates unique constraint "tableA_pkey"
DETAIL: Key (id)=(47470) already exists.
However, our UPDATE query does not affect the primary key. Here is a simplified version:
UPDATE tableA AS a
SET
items = (
SELECT array_to_string(
array(
SELECT b.value
FROM tableB b
WHERE b.a_id = b.id
GROUP BY b.name
),
','
)
)
WHERE
a.end_at BETWEEN now() AND now() - interval '1 day';
We ensured the primary key sequence was already synced:
\d tableA_id_seq
Which produces:
Column | Type | Value
---------------+---------+--------------------------
sequence_name | name | tableA_id_seq
last_value | bigint | 50364
start_value | bigint | 1
increment_by | bigint | 1
max_value | bigint | 9223372036854775807
min_value | bigint | 1
cache_value | bigint | 1
log_cnt | bigint | 0
is_cycled | boolean | f
is_called | boolean | t
Looking for maximum table index:
select max(id) from tableA;
We got a lower value:
max
-------
50363
(1 row)
Have you any idea on why such a behavior? If we exclude the problematic id, it works.
Another strange point is that replacing the previous UPDATE by:
UPDATE tableA AS a
SET
items = (
SELECT array_to_string(
array(
SELECT b.value
FROM tableB b
WHERE b.a_id = b.id
GROUP BY b.name
),
','
)
)
WHERE a.id = 47470;
It works well. Are we missing something?
EDIT: triggers
I have no user-defined triggers on this table:
SELECT t.tgname, c.relname
FROM pg_trigger t
JOIN pg_class c ON t.tgrelid = c.oid
WHERE
c.relname = 'tableA'
AND
t.tgisinternal = false
;
Which returns no row.
Note: I am using psql (PostgreSQL) 9.3.4 version.

Answer 1

Not really sure what was the cause. However, deleting the two (non vital) records corresponding to already existing ids (?) solved the issue.