[inopinatus]

> "Query over the keys without inserting a gazillion nulls into your database for rows that don't have a value for a particular key".

Having learned that postgresql NULLs are cheap in storage (since they just use a bitmap) I stopped caring much about empty column proliferation.

I've also found that arbitrary user-defined keys are still better treated via a "known keys" table, the long-term visibility into data is invaluable, there's more join flexibility, and there's opportunity to assign metadata (e.g. type hints) for each user-defined key. At scale, these things make json columns look like technical debt.

The only use case I currently have for jsonb is when the absence of an element is meaningfully different to a null value e.g. options structures that wouldn't otherwise benefit from being in normalized tables.

[ngrilly]

What is a "known keys" table?

Is it a table with columns like user_defined_text_1, user_defined_text_2, ..., user_defined_text_10, user_defined_integer_1, user_defined_integer_2, ... user_defined_integer_n ?

[inopinatus]

No, that kind of "extension table" is a well-known antipattern being fragile, unscalable, and denormalized. Just a table with columns for id, keyname & metadata about the key will do.

[ngrilly]

> No, that kind of "extension table" is a well-known antipattern being fragile, unscalable, and denormalized.

Ok, I agree. This is the reason why I was asking :-)

> Just a table with columns for id, keyname & metadata about the key will do.

Isn't this the Entity-Attribute-Value model (which has the well known drawback of requiring a join for each attribute)?

[inopinatus]

Not exactly, I wouldn't be afraid of the data table having both attribute name & value columns. EAV is practically 6NF which would prohibit that. (to be honest that id field was out of habit, the known-keys table should probably be unique and indexed on the key name)

[ngrilly]

I'm sorry, but I'm still unsure what you mean. A "known-keys table" is not a common term in the literature. Can you give an example by describing the tables and their columns?