should we also set ok to false to indicate a failure? or, how else to indicate to the caller an error occurred, and not just that there are no tables?

what about using QSet::intersect() ?
something like
QSet<QString> physical = QSet::fromList(std::transform(physicalTableNames.begin(), physicalTableNames.end(), physicalTableNames.begin(), [](const QString &s) { return s.toLower(); });_
<same for list>
QStringList results = (QSet<QString> intersect = physical.intersect(list)).toList()

This is good question for other reason. So far I assume (even documented it) that drv_getTableNames returns false only if this approach to enumerating tables is not supported by the driver. But you're right in that it would be future proof to add bool*ok to drv_getTableNames... so we can see difference between 'unsupported' and 'failure'.

It that makes sense I will rework.

Initially I tried to use QSet::intersect but we have to call toLower() on each name. Until Qt 6 has more algorithms I am not fan of converting to stl and back.
I see you proposed to convert both lists to set and only because we wanted to use intersect(). This solution has no less lines (if clang-formatted) and looks more complex. I looked at even more clever approach similar to https://stackoverflow.com/a/3396154 and it is really not worth the risk that people will not get what's happening here...

that is another case I didnt think of, but yes, could be done. I was thinking about setting the bool* ok to false that is passed into this function to tell the caller of an error.

ok

Did both things:

https://phabricator.kde.org/D11547?id=30112