SQL · Chapter 25 of 42
Date Functions
Every database has functions to extract, format and compute dates. Common ones: `NOW()`, `CURRENT_DATE`, `DATE_ADD`, `DATE_DIFF`, `EXTRACT`, `DATE_TRUNC`.
Exact names vary — check your database's docs.
Extract parts
`EXTRACT(YEAR FROM ts)`, `EXTRACT(MONTH FROM ts)` pull single fields.
Truncation
`DATE_TRUNC('month', ts)` rounds down to the first day of the month — great for time-series bucketing.
Example 1 (sql)
SELECT NOW(), CURRENT_DATE;Output
2026-07-29 12:34:00 | 2026-07-29Current timestamp and date.
Example 2 (sql)
SELECT DATE_TRUNC('month', created_at) AS month, COUNT(*)
FROM orders
GROUP BY 1
ORDER BY 1;Output
orders per monthBucket by month (Postgres syntax).
Key points
- NOW() = current timestamp.
- EXTRACT pulls a field.
- DATE_TRUNC buckets by unit.
- Store timestamps in UTC.
💡 Note: PostgreSQL `DATE_TRUNC`, MySQL `DATE_FORMAT`, SQL Server `DATEPART`/`FORMAT`. Different names, same job.