---
title: Ensure data integrity with constraints | Tiger Data Docs
description: Prevent invalid data by applying rules to your table columns using PostgreSQL constraints
---

Constraints reject invalid rows at insert or update time. On hypertables, TimescaleDB mirrors those rules to underlying chunks and keeps related indexes consistent when you add, change, or drop a constraint.

hypertables support all standard PostgreSQL constraint types. For foreign keys in particular, the following is supported:

- Foreign key constraints from a hypertable referencing a regular table
- Foreign key constraints from a regular table referencing a hypertable

Foreign keys from a hypertable referencing another hypertable **are not supported**.

For example, you can create a table that only allows positive device IDs, and non-null temperature readings. You can also check that time values for all devices are unique. To create this table, with the constraints, use this command:

```
CREATE TABLE conditions (
    time       TIMESTAMPTZ,
    temp       FLOAT NOT NULL,
    device_id  INTEGER CHECK (device_id > 0),
    location   INTEGER REFERENCES locations (id),
    PRIMARY KEY(time, device_id)
) WITH (
    tsdb.hypertable
);
```

This example also references values in another `locations` table using a foreign key constraint.

Note

Time columns used for partitioning must not allow `NULL` values. A `NOT NULL` constraint is added by default to these columns if it doesn’t already exist.

For more information on how to manage constraints, see the [PostgreSQL docs](https://www.postgresql.org/docs/current/ddl-constraints.html).