Is your feature request related to a problem?

At the moment Impala backend only supports .distinct() on a full table.

This works:

table.distinct()

This does not:

table.distinct(on=['col1', 'col2'])

Translation to backend failed
Error message: OperationNotDefinedError("Compilation rule for 'First' operation is not defined")

What is the motivation behind your request?

This forces me to write verbose workarounds.

.distinct() on a subset of a table is pretty fundamental, in my view.

Describe the solution you'd like

The on clause in .distinct() should work.

What version of ibis are you running?

10.5

What backend(s) are you using, if any?

Impala

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