As fmerges mentioned above, subselects may not work yet. What about something similar to a multi-step query then?

select max(RecordTime)
from tbl_loan
where UserId = 2
Group By LoanId
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...get that $var.

select *
from tbl_loan
where RecordTime = ?

...

$db->execute($var);
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Just a few cents, may or may not help. Just offering the idea that maybe you have to workaround it and take it as two steps.