Browsing a little history recently I came across a note I’d written about the * new-style index hint*. In that note I claimed that:

… the index has to start with the columns (product_group, id) in that order – with preference given to an exact match, otherwise using the lowest cost index that starts the right way.

On reading this statement I suddenly realised that I hadn’t actually proved (to myself, even) that if I had the indexes *(product_group, id)* and* (product_group, id, other_col)* then a two-column hint forced Oracle to use the two column index in all (legal) circumstances.

So, tonight’s quiz – are there any edge cases, and what easy ways can you think of to prove (or disprove) the claim for the general case.

**Footnote:** you don’t have to demonstrate the method, just a brief outline of the idea will be sufficient.

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