Database Reference
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You may also use this technique to provide upgrade scripts that are in fact down-
grade scripts, that is, they actually remove functionality. Be careful with this, though.
If a path to a desired version is to downgrade before an upgrade, PostgreSQL will
take the shortest route. This may result in some unintended results, including data
loss. My advice would be to not provide downgrade scripts. The risk just isn't worth
it.
