SQL ko‘rinishlar
SQL CREATE VIEW buyrug‘i
SQL ko‘rinishi (view) - bu SQL buyrug‘i natijalar to‘plamiga asoslangan virtual jadval. SQL ko‘rinishida xuddi haqiqiy jadvaldagi kabi qatorlar va ustunlar mavjud. Ko‘rinishdagi maydonlar ma’lumotlar bazasidagi bir yoki bir nechta haqiqiy jadvalning maydonlaridir.
Ko‘rinishga SQL buyruqlari va funksiyalarini qo‘shishingiz va ma’lumotlarni go‘yo bitta jadvaldan kelayotgandek taqdim etishingiz mumkin.
Ko‘rinish CREATE VIEW buyrug‘i bilan yaratilgan.
CREATE VIEW sintaksisi
CREATE VIEW view_name AS
SELECT column1, column2, ...
FROM table_name
WHERE condition;Eslatma: Ko‘rinish har doim real vaqtda ma’lumotlarni ko‘rsatadi! Ma’lumotlar bazasi mexanizmi faqat ko‘rinishning ta’rifini (SELECT buyrug‘i) saqlaydi, ma’lumotlar nusxasini emas.
KO‘RISH YARATISH Misollar
Quyidagi SQL Braziliyadagi barcha mijozlarni ko‘rsatadigan "Brazil Customers" nomli ko‘rinish yaratadi:
Misol
CREATE VIEW [Brazil Customers] AS
SELECT CustomerName, ContactName
FROM Customers
WHERE Country = 'Brazil';
Yuqoridagi ko‘rinishni so‘rash uchun quyidagi SQL sintaksisidan foydalaning:
Misol
SELECT * FROM [Brazil Customers];
Quyidagi SQL "Products Above Average Price" nomli ko‘rinishni yaratadi, u barcha mahsulotlar IN "Products" jadvalini o‘rtacha Pricedan yuqori Price bilan tanlaydi:
Misol
CREATE VIEW [Products Above Average Price] AS
SELECT ProductName, Price
FROM Products
WHERE Price > (SELECT AVG(Price) FROM Products);
Yuqoridagi ko‘rinishni so‘rash uchun quyidagi SQL sintaksisidan foydalaning:
Misol
SELECT * FROM [Products Above Average Price];
ALTER VIEW buyrug‘i (SQL Server)
IN SQL Server, ko‘rinish ALTER VIEW buyrug‘i bilan yangilanishi mumkin.
ALTER VIEW sintaksisi
ALTER VIEW view_name AS
SELECT column1, column2, ...
FROM table_name
WHERE condition;Quyidagi SQL "City" ustunini "Brazil Customers" ko‘rinishiga qo‘shadi:
Misol
ALTER VIEW [Brazil Customers] AS
SELECT CustomerName, ContactName, City
FROM Customers
WHERE Country = 'Brazil';
KO‘RISH ISHLATINI YARATISH YOKI ALSHIRISh (MySQL va Oracle)
IN MySQL va Oracle, ko‘rinish CREATE OR REPLACE VIEW iborasi bilan yangilanishi mumkin.
CREATE OR REPLACE VIEW sintaksisi
CREATE OR REPLACE VIEW view_name AS
SELECT column1, column2, ...
FROM table_name
WHERE condition;Quyidagi SQL "City" ustunini "Brazil Customers" ko‘rinishiga qo‘shadi:
Misol
CREATE OR REPLACE VIEW [Brazil Customers] AS
SELECT CustomerName, ContactName, City
FROM Customers
WHERE Country = 'Brazil';
DROP VIEW buyrug‘i
Ko‘rinish DROP VIEW buyrug‘i bilan o‘chiriladi.
DROP VIEW sintaksisi
DROP VIEW view_name;Quyidagi SQL "Brazil Customers" ko‘rinishini o‘chiradi:
Misol
DROP VIEW [Brazil Customers];
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