• Irritating because over-pedantic. Good question nevertheless.

    Thanks. The reason I felt motivated to enter it as a QOTD was that I became intrigued by the way that constraints were recorded in the metadata. Unless you appreciate the difference between a key and an index, it can be rather baffling.

    I think I ought to follow up with 'Is a Foreign Key an index? If no, is it enforced by an index?'

    Best wishes,
    Phil Factor