you can, but in order to build a partial index, the function needs to be immutab... | Hacker News

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		jerrysievert on June 4, 2012 \| parent \| context \| favorite \| on: Building a MongoDB Clone in Postgres you can, but in order to build a partial index, the function needs to be immutable. not exactly ideal in this case.

rosser on June 4, 2012 [–]

Immutability is perfectly appropriate for that use-case, though. Creating an index via a function that may return different outputs when provided the same input is always going to lose.

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