Difference between two dates

-- Postgres / DuckDB / Oracle: plain subtraction returns days.
SELECT (end_date - start_date) AS days FROM events;

-- SQLite needs julianday().
SELECT julianday(end_date) - julianday(start_date) AS days FROM events;

-- DATEDIFF (and BigQuery's DATE_DIFF). Argument order varies:
SELECT DATEDIFF(end_date, start_date) AS days FROM events;          -- MySQL — always days
SELECT DATEDIFF(DAY, start_date, end_date) AS days FROM events;     -- SQL Server / Snowflake / Redshift
SELECT DATE_DIFF(end_date, start_date, DAY) AS days FROM events;    -- BigQuery (different name)

-- Months or years.
SELECT DATEDIFF(MONTH, start_date, end_date) AS months FROM events; -- SQL Server / Snowflake
SELECT AGE(end_date, start_date) AS interval FROM events;           -- Postgres (returns INTERVAL)
SELECT MONTHS_BETWEEN(end_date, start_date) AS months FROM events;  -- Oracle

-- Days between (works in all major engines via subtraction or DATEDIFF).
SELECT DATEDIFF(DAY, '2026-01-01', '2026-04-26') AS days;     -- SQL Server / Snowflake -> 115
SELECT DATE_DIFF('day', DATE '2026-01-01', DATE '2026-04-26') -- DuckDB only
       AS days;
SELECT DATE '2026-04-26' - DATE '2026-01-01' AS days;         -- Postgres / DuckDB

-- Whole calendar months between (counts month boundaries crossed, not "30-day chunks").
SELECT DATEDIFF(MONTH, '2026-01-31', '2026-02-01') AS months; -- SQL Server -> 1 (one month boundary)

-- Hours / minutes / seconds (TIMESTAMP inputs).
SELECT DATEDIFF(HOUR, started_at, ended_at)   AS hrs   FROM jobs; -- SQL Server / Snowflake
SELECT DATE_DIFF('minute', started_at, ended_at) AS mins FROM jobs; -- DuckDB
SELECT EXTRACT(EPOCH FROM (ended_at - started_at)) / 60 AS mins
       FROM jobs; -- Postgres