> ## Documentation Index
> Fetch the complete documentation index at: https://docs.omniql.com/llms.txt
> Use this file to discover all available pages before exploring further.

# Advanced Schema

> Column constraints

## Column Constraints

OmniQL supports three column constraints using colon syntax:

```sql theme={}
:CREATE TABLE User WITH
  id:AUTO,
  email:STRING:NOTNULL:UNIQUE,
  name:STRING:NOTNULL
```

| Constraint  | Syntax        | Effect                |
| ----------- | ------------- | --------------------- |
| Not Null    | `:NOTNULL`    | Column cannot be NULL |
| Unique      | `:UNIQUE`     | Values must be unique |
| Primary Key | `:PRIMARYKEY` | Column is primary key |

### Multiple Constraints

Chain multiple constraints with colons:

```sql theme={}
:CREATE TABLE Product WITH
  id:AUTO,
  sku:STRING:NOTNULL:UNIQUE,
  name:STRING:NOTNULL,
  price:DECIMAL
```

| Database   | Output                                                                                                                                   |
| ---------- | ---------------------------------------------------------------------------------------------------------------------------------------- |
| PostgreSQL | `CREATE TABLE products (id SERIAL PRIMARY KEY, sku VARCHAR NOT NULL UNIQUE, name VARCHAR NOT NULL, price DECIMAL)`                       |
| MySQL      | `CREATE TABLE products (id INT AUTO_INCREMENT PRIMARY KEY, sku VARCHAR(255) NOT NULL UNIQUE, name VARCHAR(255) NOT NULL, price DECIMAL)` |

## Database-Specific Features

For advanced features like sequences, custom types, triggers, and stored procedures, see database-specific documentation:

* [PostgreSQL Features](/databases/postgresql) - Sequences, ENUM types, domains, triggers, policies
* [MySQL Features](/databases/mysql)
* [MongoDB Features](/databases/mongodb)
* [Redis Features](/databases/redis)

## Limitations

Not supported in OmniQL (use native SQL):

* CHECK constraints
* Foreign key references (REFERENCES)
* ON DELETE / ON UPDATE actions
* DEFAULT values
* Composite primary keys

## Next Steps

<CardGroup cols={2}>
  <Card title="PostgreSQL" icon="database" href="/databases/postgresql">
    PostgreSQL-specific features
  </Card>

  <Card title="Transactions" icon="arrows-rotate" href="/control/transactions">
    Group operations safely
  </Card>
</CardGroup>