RestoreBackgroundImageColor background job causes database error

[nickvergessen]

Error while running background job OCA\Theming\Jobs\RestoreBackgroundImageColor

An exception occurred while executing a query:
SQLSTATE[42601]: Syntax error: 7 ERROR:  
syntax error at or near
"" FROM "" LINE 1: ..."oc_preferences" "a" LEFT JOIN "oc_(SELECT "userid" FROM "oc...
                                                         ^

The syntax created by

server/apps/theming/lib/Jobs/RestoreBackgroundImageColor.php

Line 72 in 9836e9b

->leftJoin('a', $qb->createFunction('(' . $innerSQL->getSQL() . ')'), 'b', 'a.userid = b.userid')

is invalid

• I added a unit test to demonstrate it in test(theming): Add unit test to check database query in theming backgroundjob #53778

It's basically failing this check in oracle and when sharding is used:

server/lib/private/DB/QueryBuilder/QueryBuilder.php

Lines 1331 to 1333 in 48d69c7

	if ($table instanceof IQueryFunction) {
	return (string)$table;
	}

[nickvergessen]

I think this actually needs changes in the PartitionedQueryBuilder, as it should support the general syntax as well?

[nickvergessen]

Actually the problem origins from the (string) cast here:

server/lib/private/DB/QueryBuilder/Partitioned/PartitionedQueryBuilder.php

Line 208 in 5981b7e

return $this->join($fromAlias, (string)$join, $alias, $condition, PartitionQuery::JOIN_MODE_LEFT);

cc @icewind1991 @susnux