3 Logic Errors You Can Finally Delete Using Postgres Range Types and EXCLUDE Constraints

I spent an embarrassing amount of my early career writing massive, brittle WHERE clauses to make sure two events didn't overlap in a database. You know the ones—the logic puzzles where you're comparing start_time and end_time using four different operators, praying you didn't miss a "greater than or equal to" somewhere. It felt like I was writing high school algebra instead of building a feature.

Then I found out Postgres already solved this. Not with more code, but with Range Types.

If you're still treating two columns (like start_date and end_date) as separate entities, you’re basically inviting bugs to dinner. Here are three logic errors you can delete from your codebase right now by switching to native ranges and EXCLUDE constraints.

1. The "Double-Booked" Race Condition

The most common way developers handle scheduling is by checking for overlaps in the application code. It looks something like this:

1. Query the DB: "Is there anything between 2:00 PM and 3:00 PM?"
2. If the result is empty, send an INSERT.

The problem? If two users click "Book Now" at the exact same millisecond, both queries might return empty. You end up with two people booked for the same room at the same time.

Postgres lets you offload this entire problem to the database engine using an EXCLUDE constraint. It’s like a UNIQUE constraint, but for overlaps.

CREATE EXTENSION IF NOT EXISTS btree_gist;

CREATE TABLE conference_rooms (
    room_id text,
    reservation_period tstzrange,
    -- This is the magic part:
    EXCLUDE USING gist (
        room_id WITH =, 
        reservation_period WITH &&
    )
);

The && operator is the "overlaps" operator. By adding this constraint, Postgres will physically prevent any row from being inserted if its reservation_period overlaps with an existing one for that room_id. No race conditions, no manual checks, no stress.

2. The "Off-By-One" Boundary Headache

Is the end time inclusive or exclusive? If a meeting ends at 3:00 PM, can the next one start exactly at 3:00 PM, or does it have to be 3:01 PM?

When you use two separate columns, you're constantly fighting with < vs <=. Postgres range types use standard mathematical notation: [ or ] for inclusive, and ( or ) for exclusive.

By default, Postgres uses [ ) (inclusive start, exclusive end). This is the "sane" way to handle time.

-- This creates a range from 2:00 to 3:00. 
-- It includes 2:00:00.000, but excludes 3:00:00.000.
SELECT tstzrange('2023-10-01 14:00:00Z', '2023-10-01 15:00:00Z');

-- If you try to see if they overlap:
SELECT tstzrange('14:00', '15:00') && tstzrange('15:00', '16:00');
-- Result: FALSE. 

Because the first range *excludes* 3:00 PM and the second *includes* it, there is zero overlap. You don't have to write logic to subtract one millisecond from your "end" times anymore. The database understands the continuity of time better than your if/else statements do.

3. The "Gaps in History" Logic Error

If you're building something like a pricing table or a subscription system, you often need to ensure that for any given time, there is exactly one active record. You don't want a "gap" where a product has no price, and you definitely don't want two prices active at once.

Checking for these "holes" in your data with standard timestamp columns is a nightmare of window functions and LAG().

With range types, you can use the adjacency operator (-|-) to find records that sit perfectly flush against each other, or use functions to "merge" ranges together.

-- Are these two ranges perfectly adjacent?
SELECT '[2023-01-01, 2023-01-02)'::daterange -|- '[2023-01-02, 2023-01-03)'::daterange;
-- Result: TRUE

If you need to find if a specific timestamp is covered by a range, use the "contains" operator (@>):

SELECT * FROM subscription_plans 
WHERE active_period @> '2023-10-25 10:00:00'::timestamptz;

This reads like English: "Where the active period contains this timestamp." It's indexed, it's fast, and it's virtually impossible to mess up.

The "Gotcha" (Because there's always one)

Before you go off and refactor everything, remember that EXCLUDE constraints require the gist index type. If you are filtering by a simple ID (like room_id in my first example) inside that constraint, you'll need the btree_gist extension enabled.

Most managed Postgres providers (RDS, Supabase, etc.) have this pre-installed; you just need to run CREATE EXTENSION btree_gist;.

Summary: Stop Doing the DB's Job

We often treat the database as a dumb bucket for data and try to handle all the "smart" logic in our application code. But Postgres is built for data integrity.

By using tstzrange, daterange, or int4range, you move the "source of truth" for your business logic into the layer that actually persists the data. You get:
- Atomicity: No more race conditions.
- Clarity: && is way easier to read than four lines of comparison logic.
- Performance: GIST indexes for ranges are incredibly optimized.

Next time you find yourself writing WHERE start_date <= ? AND end_date >= ?, take a breath, delete it, and let Postgres handle the heavy lifting.