Every JSON Column Has a Schema

Architected by Chet, written by Antigravity

Let's complete the trilogy (That's probably a lie...).

Over the last two weeks, we've picked apart the boolean:

• In the warehouse (OLAP), a boolean duplicates a truth that already exists elsewhere (your temporal boundaries).
• In an operational system (OLTP), a boolean destroys a truth that did exist (wiping out history and sequence).

A JSON column does something far sneakier: it never declares a truth, so nothing can ever contradict it.

The Unfalsifiable Blob

A shapeless blob cannot be wrong, because there is no declared shape for it to violate.

Think about what happens when you create a proper relational column. You declare customer_id INTEGER NOT NULL REFERENCES customers(id). You have drawn a hard line in the sand. If the application tries to insert 'banana', the database rejects it. If it tries to insert an orphaned customer, the database rejects it. The engine knows what is true and what is a lie, and it protects you.

Now look at a JSON column.

• {"customer_id": 123} is valid JSON.
• {"customer_id": "123"} is valid JSON.
• {"customerId": null} is valid JSON.
• {"cust_id": "banana"} is valid JSON.
• {} is valid JSON.

The database accepts every single one of those rows without blinking. It writes them to disk, returns a 200 OK, and goes about its day. Why? Because you never declared a contract. You never told the database what "right" looks like, so nothing can ever be "wrong."

Until six months later, when the reporting query blows up. At that point, you don't have a data model: you have vibes and a support ticket.

Watching From the Outside

I know why people do it. A new feature lands on your desk, the product manager is still fuzzy on the specs, the attributes will probably change next sprint, and you just need to get the code out the door. So you slap a payload JSON column on the table and tell yourself you're being agile.

I've never done this. Not with JSON.

Booleans, sure. I will readily admit to that sin. I've slapped an is_active flag on a table and paid for it later. But dumping application objects into a JSON column is one I have only ever watched from the outside, which is its own kind of education.

If you come from the database world, the foundational rule has always been simple: put integrity constraints as close to the data as humanly possible. The database exists to protect the data from the application, because applications get rewritten every two years, but data lives forever.

When you drop an unconstrained JSON blob into a table, you're betting that every future engineer touching that application will remember to enforce every single implicit business rule in code.

Spoiler: they won't.

Rebuilding the Schema, Badly

Someone reading this will inevitably push back: "Wait, you can enforce integrity on a JSON column!"

And you can. Modern engines will let you bolt integrity back onto a document. Postgres will happily take a CHECK constraint on an extracted jsonb path. You can create generated columns with foreign keys, and you can build functional GIN or B-tree indexes against nested attributes.

Technically, you can do it. But look at what you are actually doing: you are reconstructing, one painful piece at a time, the relational schema you declined to write in the first place, using an esoteric, vendor-specific syntax that nobody on your team will recognize in a year.

You didn't avoid the schema. You just decided to rebuild a worse version of it by hand.

Relocating the True Cost (and Closing the Loop)

To be clear: this isn't about beating up on application developers.

When a developer drops a JSON column into a migration, they aren't trying to sabotage the company. They are responding to very real, very rational pressures: sprint deadlines, velocity metrics, and avoiding the friction of formal schema reviews. From their seat in the sprint, skipping the table design feels like pure efficiency.

Years ago, Cary Millsap wrote a post about formatting tables of numbers that contained an insight I have quoted many times:

"Good design is a topic of consideration. And even conservation. If spending 10 extra minutes formatting your data better saves 1,000 readers 2 minutes each, then you’ve saved the world 1,990 minutes of wasted effort."

Cary's math is irrefutable, but appealing to civic virtue ("save the world 1,990 minutes") rarely changes engineering behavior on its own. What actually changes behavior is seeing the feedback loop close.

When you dump a raw, shapeless JSON blob into a table, you didn't eliminate the work. You simply relocated the cost.

In the short term, you quietly transferred that cost downstream to the analytics engineers and BI developers. Every single report now requires defensive SQL: unnesting arrays, casting strings to integers, guessing at nulls, and handling three different key spellings.

But the loop doesn't stop with the analytics team.

Eventually, product asks for a new operational feature: an in-app filter, a bulk edit, or a performance dashboard built directly against that transactional table. And guess who gets assigned the ticket? The application developer.

Now, the very engineer who bypassed the schema to save twenty minutes in sprint four is staring at a production bug in sprint twelve, trying to write unreadable JSON path queries against their own shapeless blob. You didn't save time. You just deferred the agony, with interest, back onto your future self.

The Waiver

In my own agent instructions, a JSON column requires a waiver: the default answer is no, and the burden of proof is on the column.

When does it actually earn that waiver?

When the data is genuinely an opaque, third-party black box that the database never needs to reason about: raw webhook payloads, audit logs, or configuration blobs that the engine will never filter, join, or aggregate on.

If your application needs to query it, if your business needs to report on it, or if it relates to any other entity in your system: it belongs in a column.

Doh. It really is that simple.