SQLda takrorlanadigan user_id va device_id bilan yagona qiymat juftlarini qanday hisoblash mumkin?

SQL-da, user_id va device_id takrorlanishi mumkin bo'lgan holda, (user_id, device_id) unikal juftlarning sonini hisoblash uchun COUNT(DISTINCT ...) konstruktsiyasidan foydalanish kerak. Masalan:

SELECT COUNT(DISTINCT user_id, device_id) AS unique_pairs_count
FROM your_table;

Ba'zi ma'lumotlar bazasi boshqaruv tizimlarida, masalan PostgreSQL-da, bu sintaksis to'g'ridan-to'g'ri qo'llab-quvvatlanadi. Agar ma'lumotlar bazasi COUNT(DISTINCT) bilan bir nechta ustunni qo'llab-quvvatlamasa, qiymatlarni yagona satrga birlashtirish mumkin:

SELECT COUNT(DISTINCT CONCAT(user_id, '_', device_id)) AS unique_pairs_count
FROM your_table;

Yoki guruhlash bilan subquery ishlatish:

SELECT COUNT(*) AS unique_pairs_count
FROM (
  SELECT user_id, device_id
  FROM your_table
  GROUP BY user_id, device_id
) AS unique_pairs;

Bu, user_id va device_id kombinatsiyalarining unikal sonini olish imkonini beradi.