# Choose a primary key

A primary key identifies a row. Choose values that remain stable when other row fields change, and make additional business identifiers UNIQUE when they also need duplicate protection.

## Ordinary integer identity

In an ordinary rowid table, a column declared exactly `INTEGER PRIMARY KEY` aliases the row identifier. Other native integer declarations, such as `UInt64 PRIMARY KEY`, do not have that alias contract.

Use UNIQUE constraints or unique indexes for additional keys. These constraints enforce uniqueness; a ClickHouse sorting-key or sparse-index contract does not apply.

## Compound identity

A table-level PRIMARY KEY can contain several columns. A WITHOUT ROWID table uses that declared key as its row identity:

```sql
CREATE TABLE readings
(
    sensor UInt32,
    day Date32,
    value Float64,
    PRIMARY KEY(sensor, day)
) WITHOUT ROWID;
INSERT INTO readings VALUES (7, '2025-03-05', 12.5);
```

```sql
SELECT sensor, day, value
FROM readings
FORMAT csv;
```

```text
7,"2025-03-05",12.5
```

This key allows one reading per sensor and day. Declare explicit NOT NULL constraints where the row's identity must never be missing under ordinary table nullability rules.

See [`CREATE TABLE`](https://coordinatordb.com/docs/reference/statements/create/table) and [`CREATE INDEX`](https://coordinatordb.com/docs/reference/statements/create/create-index).