Predict, then run it

pings(t) = 0, 30 (minutes), with a 30-minute timeout. If an exactly-30-minute gap should keep the pings in one session, the boundary operator is '>':

SELECT SUM(CASE WHEN gap > 30 THEN 1 ELSE 0 END) AS new_sessions FROM (SELECT t - LAG(t) OVER (ORDER BY t) AS gap FROM pings) WHERE gap IS NOT NULL;

Predict the exact output.