Databases always have a schema (2018)

Re:Databases always have a schema (2018) by nathan_long on Monday February 25, 2019 @04:02PM (#19249433)

I would argue that it's not authoritative. Nothing guarantees that the records in the db match that schema; the closest you get to a guarantee is your diligence to 1) run a job mutating all records every time you change your in-code schema and 2) ensure that nothing but your latest application code can write to the db.

OTOH, `\d users` in PostgreSQL is authoritative; there cannot be a row that does not conform to the fields, types, and constraints listed there.

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Re:Databases always have a schema (2018) by jt2190 on Monday February 25, 2019 @05:27PM (#19250084)

> I would argue that it's not authoritative.

I think the word you're looking for is "enforced". Where there are multiple schemas, one can certainly be the "authority", even if it's not enforced across all data.

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Re:Databases always have a schema (2018) by nathan_long on Tuesday February 26, 2019 @10:10AM (#19254843)

Whatever terminology you use, every place you loop through records doing stuff with them, you'll either have to decide what to do with oddly-shaped records or implicitly decide to let exceptions occur at that point. Whereas if PostgreSQL tells you that `user` has a `email character varying(255) NOT NULL`, you can be sure that every `user` does. The only place you need a conditional related to that is when trying to insert an invalid record.

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