PostgreSQL HAVING
EGA
HAVING bandi SQL’ga qo‘shilgan, chunki WHERE bandini agregat funksiyalar bilan ishlatib bo‘lmaydi.
Agregat funksiyalar ko‘pincha GROUP BY bandi bilan qo‘llaniladi va HAVING qo‘shish orqali biz WHERE bandidagi kabi shart yozishimiz mumkin.
Misol
Faqat 5 martadan ortiq vakili bo‘lgan davlatlarni sanab o‘ting:
SELECT COUNT(customer_id), country
FROM customers
GROUP BY country
HAVING COUNT(customer_id) > 5;
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Ko‘proq misollar
Quyidagi SQL operatorida faqat umumiy narxi 400$ yoki undan yuqori bo‘lgan buyurtmalar ro‘yxati keltirilgan:
Misol
SELECT order_id, SUM(order_details.quantity * products.price)
FROM order_details
LEFT JOIN products on products.product_id = order_details.product_id
GROUP BY order_id
HAVING SUM(order_details.quantity * products.price) > 400.00;
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1000$ yoki undan ortiq tartib bergan mijozlar ro‘yxati:
Misol
SELECT customers.customer_name,
SUM(order_details.quantity * products.price)
FROM order_details
INNER JOIN products ON order_details.product_id = products.product_id
INNER JOIN orders ON order_details.order_id = orders.order_id
INNER JOIN customers ON orders.customer_id = customers.customer_id
GROUP BY customers.customer_id, customers.customer_name
HAVING SUM(order_details.quantity * products.price) >= 1000;
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