SQL EXISTS operatori

EXISTS operatori WHERE bandida quyi so‘rov biror qator qaytarish-qaytarmasligini tekshirish uchun ishlatiladi.

EXISTS operatori agar quyi so‘rov kamida bitta qatorni qaytarsa, TRUE, aks holda FALSE deb baholaydi.

EXISTS sintaksisi

SELECT column_name(s)
FROM table_name
WHERE EXISTS (subquery);

Demo ma’lumotlar bazasi

Quyida Northwind namunaviy ma’lumotlar bazasidagi "Products" jadvalidan tanlanma keltirilgan:

ProductID	ProductName	SupplierID	CategoryID	Unit	Price
1	Chais	1	1	10 boxes x 20 bags	18.00
2	Chang	1	1	24 - 12 oz bottles	19.00
3	Aniseed Syrup	1	2	12 - 550 ml bottles	10.00
4	Chef Anton's Cajun Seasoning	2	2	48 - 6 oz jars	22.00
5	Chef Anton's Gumbo Mix	2	2	36 boxes	21.35

Va tanlanma "Suppliers" jadvali:

SupplierID	SupplierName	ContactName	Address	City	PostalCode	Country
1	Exotic Liquid	Charlotte Cooper	49 Gilbert St.	London	EC1 4SD	UK
2	New Orleans Cajun Delights	Shelley Burke	P.O. Box 78934	New Orleans	70117	USA
3	Grandma Kelly’s Homestead	Regina Murphy	707 Oxford Rd.	Ann Arbor	48104	USA
4	Tokyo Traders	Yoshi Nagase	9-8 Sekimai Musashino-shi	Tokyo	100	Japan

SQL EXISTS misollari

Quyidagi SQL narxi 10 dan past bo‘lgan mahsulotga ega yetkazib beruvchilar bor-yo‘qligini tekshiradi. Agar quyi so‘rov TRUE deb baholansa, mahsulot narxi 10 dan kam bo‘lgan yetkazib beruvchilar ro‘yxati chiqariladi:

Misol

SELECT SupplierName
FROM Suppliers
WHERE EXISTS (
SELECT ProductName
FROM Products
WHERE Products.SupplierID = Suppliers.supplierID AND Price < 10
);

O‘zingiz sinab ko‘ring »

Quyidagi SQL narxi 22 ga teng mahsulotga ega yetkazib beruvchilar bor-yo‘qligini tekshiradi. Agar quyi so‘rov TRUE deb baholansa, mahsulot narxi 22 ga teng bo‘lgan yetkazib beruvchilar ro‘yxati chiqariladi:

Misol

SELECT SupplierName
FROM Suppliers
WHERE EXISTS (
SELECT ProductName
FROM Products
WHERE Products.SupplierID = Suppliers.supplierID AND Price = 22
);

O‘zingiz sinab ko‘ring »

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