Kirish Ma’lumotlar bazasi haqida mbbt funktsityalari

Chet el kalitini qo'shish

Aytaylik, dastlab ma'lumotlar bazasiga hech qanday tarzda bog'lanmagan ikkita jadval qo'shilgan:

CREATE TABLE Customers ( Id INT PRIMARY KEY IDENTITY, Age INT DEFAULT 18, FirstName NVARCHAR(20) NOT NULL, LastName NVARCHAR(20) NOT NULL, Email VARCHAR(30) UNIQUE, Phone VARCHAR(20) UNIQUE ); CREATE TABLE Orders ( Id INT IDENTITY, CustomerId INT, CreatedAt Date );

Buyurtmalar jadvalining CustomerId ustuniga xorijiy kalit cheklovini qo'shing:

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ALTER TABLE Orders ADD FOREIGN KEY(CustomerId) REFERENCES Customers(Id);

Asosiy kalitni qo'shish

Yuqorida belgilangan Buyurtmalar jadvalidan foydalanib, unga Id ustuni uchun asosiy kalitni qo'shamiz:

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ALTER TABLE Orders ADD PRIMARY KEY (Id);

Ismlar bilan cheklovlar qo'shish

Cheklovlarni qo'shganda biz ular uchun CONSTRAINT iborasidan keyin cheklov nomidan foydalanib nom belgilashimiz mumkin:

ALTER TABLE Orders ADD CONSTRAINT PK_Orders_Id PRIMARY KEY (Id), CONSTRAINT FK_Orders_To_Customers FOREIGN KEY(CustomerId) REFERENCES Customers(Id); ALTER TABLE Customers ADD CONSTRAINT CK_Age_Greater_Than_Zero CHECK (Age > 0);