Language reference
HOUR (extract hour)
Syntax
HOUR(<time-or-timestamp>)
γ HOUR(occurred_at) → hr, COUNT(id) → hits (Events)Description
HOUR pulls the hour-of-day (0–23) out of a time or timestamp. Use it to bucket activity by hour — traffic by time of day, peak-hour analysis.
Technical Description
HOUR(t) → NUMBER (0–23). Accepts a TIME or TIMESTAMP (a TIMESTAMP is read at UTC); other types are an evaluation error. NULL input returns NULL. PURE, DETERMINISTIC.
Examples
Hits per hour of day:
γ HOUR(occurred_at) → hr, COUNT(id) → hits (Events)GROUP HOUR(occurred_at) -> hr, COUNT(id) -> hits (Events)Overnight records:
σ HOUR(logged_at) < 6 (Logs)SELECT HOUR(logged_at) < 6 (Logs)Pushdown
SQL: folds to EXTRACT(HOUR FROM <col>) on every dialect but SQLite, which has no date type to extract from. On SQL Server, which has no EXTRACT, it is DATEPART(HOUR, SWITCHOFFSET(<col>, '+00:00')) — the value switched to UTC first, so a DATETIMEOFFSET is read at UTC as the engine reads it. MongoDB: folds to {"$hour": "$<col>"} inside a $project stage (requires alias).
Limitations
Argument must be a TIME or TIMESTAMP. Returns 0–23. TIMESTAMP at UTC. NULL in → NULL out.