116. EXISTS va IN — qayta yozish

Kamida bir marta Pizza turkumidagi restorandan buyurtma qilgan

mijozlarni toping.

Bu masalani ikki xil yozish mumkin:

WHERE c.id IN (SELECT o.client_id FROM ...)      -- IN shakli
WHERE EXISTS (SELECT 1 FROM ... WHERE o.client_id = c.id)  -- EXISTS shakli

Bu yerda client_id hech qachon NULL emas, shuning uchun ikkalasi ham

bir xil natija beradi. Ikkalasini ham yozib ko'ring — judge natijani

tekshiradi, shaklini emas.

Ustunlar: id, name.

Saralash: id o'sish.

clients: id INT PK, name VARCHAR

restaurants: id INT PK, title VARCHAR, kind VARCHAR

orders: id INT PK, client_id INT NOT NULL, restaurant_id INT NOT NULL