EXISTS Operator

SQL EXISTS Operatori

EXISTS operatori bir subso'rovda har qanday yozuv mavjudligini tekshirish uchun ishlatiladi.

EXISTS operatori subso'rov bir yoki bir nechta yozuv qaytarsa, TRUE qiymatini qaytaradi.

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

Ushbu o'quv qo'llanmada Northwind namunaviy ma'lumotlar bazasidan "Products" jadvalidan bir tanlov:

ProductID	ProductName	SupplierID	CategoryID	Unit	Price
1	Chais	1	1	10 boxes x 20 bags	18
2	Chang	1	1	24 - 12 oz bottles	19
3	Aniseed Syrup	1	2	12 - 550 ml bottles	10
4	Chef Anton's Cajun Seasoning	2	2	48 - 6 oz jars	22
5	Chef Anton's Gumbo Mix	2	2	36 boxes	21.35

Va "Suppliers" jadvalidan bir tanlov:

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

Quyidagi SQL bayonoti TRUE qaytaradi va narxi 20 dan kam bo'lgan mahsulotga ega yetkazib beruvchilarni ro'yxatga oladi:

SELECT SupplierName
FROM Suppliers
WHERE EXISTS (SELECT ProductName FROM Products WHERE Products.SupplierID = Suppliers.SupplierID AND Price < 20);

Quyidagi SQL bayonoti TRUE qaytaradi va narxi 22 ga teng bo'lgan mahsulotga ega yetkazib beruvchilarni ro'yxatga oladi:

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