is this an SQL injection - postgresql

Question

In the apache access logs I found the following code as query string (GET), submitted multiple times each second for quite a while from one IP:
**/OR/**/ASCII(SUBSTRING((SELECT/**/COALESCE(CAST(LENGTH(rn)/**/AS/**/VARCHAR(10000))::text,(CHR(32)))/**/FROM/**/"public".belegtable/**/ORDER/**/BY/**/lv/**/OFFSET/**/1492/**/LIMIT/**/1)::text/**/FROM/**/1/**/FOR/**/1))>9
What does it mean?
Is this an attempt of breaking in via injection?
I have never seen such a statement and I don't understand its meaning. PostgreSQL is used on the server.
rn and belegtable exist. Some other attempts contain other existing fields/tables. Since the application is very costum, I don't know how the information on existing SQL fields can be known to strangers. Very weird.

Answer 1

**/
OR ASCII(
SUBSTRING(
( SELECT COALESCE(
CAST(LENGTH(rn) AS VARCHAR(10000))::text,
(CHR(32))
)
FROM "public".belegtable
ORDER BY lv
OFFSET 1492
LIMIT 1
)::text
FROM 1
FOR 1
)
) > 9
Is this an attempt of breaking in via injection?
The query in question does not have too many characteristics of an attempted SQL injection.
An SQL injection typically involves inserting an unwanted action into some section of a bigger query, under the disguise of a single value. Typically the injected part tries to guess what comes before it, neutralise it, do something malicious and secure the entire query from syntax errors by also neutralising what comes after the injected piece, which might not be visible to the attacker.
I don't see anything that could work as an escape sequence at the beginning or anything that would neutralise the remains of the query coming in after the injection. What this query does also isn't malicious. An SQL injection would attempt to extract some additional information about the database security, structure and configuration, or - if the attacker already gathered enough data - it would try to steal the data, encrypt it or tamper with it otherwise, depending on the aim and strategy of the attacker as well as the type of data found in the database. There also wouldn't be much point looping it like that.
As to the looping part: if someone attempted to put load on the database - as in DDoS - you'd likely see more than one node doing that and probably in a more elaborate and well disguised manner, using different and more demanding queries sent at different frequencies.
What does it mean?
It's likely someone's buggy code stuck in an unterminated loop, judging by the LIMIT and OFFSET mechanism I've seen used for looping through some set of records by taking one at a time (LIMIT 1) and incrementing which one to get next (OFFSET n). The whole expression always returns true because ASCII() returns the character code of the first character in the string. That string defaults to a space ' ', ASCII code 32, or some text representation of a number between 0 and 99999. Sice all ASCII digits are between code 48 and 57, it's effectively always comparing some bigger number than 9 to a 9, checking if it indeed is bigger.
The author of that code might not have predicted the loop to be able to run infinitely and might have misinterpreted what some of the functions used in that query do. Regardless of what really happened, I think it was a good idea to cut off that IP avoiding needless stress on the database. Double-checking your security setup is always a good idea but I wouldn't call this an attempted attack. At least not this query alone, as it might be a harmless piece of a bigger, more malicious operation - but that could be said about any query.