리텐션 아래와 같은 방식으로 리텐션과 리텐션율을 계산할 수 있 SELECT retention_test.date, count() AS initial_users, countIf(arrayExists(d -> d = retention_test.date + 1, dates)) AS day1, countIf(arrayExists(d -> d = retention_test.date + 2, dates)) AS day2, countIf(arrayExists(d -> d = retention_test.date + 3, dates)) AS day3, countIf(arrayExists(d -> d = retention_test.date + 4, dates)) AS day4, countIf(arrayExists(d -> ..