While I believe that the city should share the schema, and that the city is effectively argues for security through obscurity, I disagree with the main premise of the article: that knowing SQL schema doesn't help the attacker.
If I understand the argument of the author here:
> Attackers like me use SQL injection attacks to recover SQL schemas. The schema is the product of an attack, not one of its predicates
The author appears to imply that once the vulnerability is found, the schema can be recovered anyway. It is not always the case. It is perfectly viable to find a SQL injection that would allow to fetch some data from the table that is being queried, but not from any other table, including `information_schema` or similar. If all the signal you get from the vunlerability is also "query failed" or "query succeeded, here's the data", knowing the schema makes it much easier to exploit.
> the problem is that every computer system connected to the Internet is being attacked every minute of every day
If you specifically log failed DB queries, than for all the possible injections that such 24/7 attacks would find you have already patched them. The log would then be not deafening until someone stumbles on the actual injection (that, for example, only exists for logged in users, and thus is not found by bots), in which case you have time to see it and patch before the attacker finds a way to actually utilize it.
Knowing schema both expedites their ability to take advantage of the vulnerability, but also increases their chances of probing the injection without triggering the query failure to begin with.