# Query dated measurements

Store a measurement's time, identity and value in declared columns. Choose `Date` for a calendar day or a documented timestamp type when time of day matters. State the timezone convention before comparing or aggregating timestamps.

```sql
CREATE TABLE daily_measurements(day Date, sensor_id INTEGER, value Float64);
INSERT INTO daily_measurements VALUES
    ('2025-01-01', 1, 10.0), ('2025-01-01', 1, 14.0),
    ('2025-01-02', 1, 12.0);

SELECT day, sensor_id, count(*) AS samples, avg(value) AS mean_value
FROM daily_measurements
GROUP BY day, sensor_id
ORDER BY day, sensor_id;
```

This query groups available rows. A day with no measurement does not appear automatically. Use a generated calendar or another date relation when a report must distinguish missing observations from a measured zero.

Use half-open ranges for adjacent reporting periods so their shared boundary is not counted twice. A targeted index can help repeated time-and-identity lookups; inspect the actual plan before keeping it. Retention is an explicit `DELETE` task, not automatic TTL processing.

See [Date](https://coordinatordb.com/docs/reference/data-types/date), [DateTime](https://coordinatordb.com/docs/reference/data-types/datetime), [series generation](https://coordinatordb.com/docs/reference/functions/table-functions/generate-series) and [retention](https://coordinatordb.com/docs/resources/support-center/knowledge-base/data-management/when-is-ttl-applied).