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0 pointsbazoom422y ago0 comments

A lot of confusion comes from SQL nulls having the same name as nulls in programming languages. They are conceptually completely different things.

Nulls in programming languages are a special “sentinel” value indicating the lack of an object. Nulls in sql means “unknown” or “I am not able to answer that question”.

This is why in most programming languages two nulls are equal, since they are the same sentinel value. Not so in SQL, since one unknown value is not necessaily the same as some other unknown value.

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4 comments · 1 top-level

dspillett2y ago· 3 in thread

Worse: with JSON NULL is considered a type not a value of other types, which can make validating nullable values with JSON-Schema a royal pain.

bazoom42OP2y ago

JSON does not define a type system, but javascript defines null as the only value of the null type. This works fine in eg typescript since you can use a type union of null and any other type, if you want to indicate a nullable value.

Izkata2y ago

Don't forget in addition to null, javascript has undefined and undefined.

(the value undefined and the property-does-not-exist undefined)

VMG2y ago

but don't forget that `typeof null === 'object'` :)

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