Comment by Sesse__

This isn't really the same as MySQL's ICP; it seems more like what MySQL would call a “ref” or “eq_ref” lookup, i.e. a simple lookup on an indexed value on the right side of a nested-loop join. It's bread and butter for basically any database optimizer.

ICP in MySQL (which can be built on top of ref/eq_ref, but isn't part of the normal index lookup per se) is a fairly weird concept where the storage engine is told to evaluate certain predicates on its own, without returning the row to the optimizer. This is to a) reduce the number of round-trips (function calls) from the executor down into the storage engine, and b) because InnoDB's secondary indexes need an extra storage round-trip to return the row (secondary indexes don't point at the row you want, they contain the primary key and then you have to lookup the actual row from the PK), so if you can remove the row early, you can skip the main row lookup.