1-mavzu. Ma’lumotlar bazasi obyektlarini yaratish

CHECK
CHECK kalit so`zi ustunda saqlanishi mumkin bo'lgan qiymatlar chegarasini belgilaydi. Buning uchun CHECK so`zidan so'ng, qavs ichida shart ko`rsatiladi, ustun yoki bir nechta ustunlardagi qiymatlar shartga javob berishi kerak. Masalan, mijozlarning yoshi 0 dan kam yoki 100 dan yuqori bo'lishi mumkin emas:
CREATE TABLE Customers
(
Id INT PRIMARY KEY IDENTITY,
Age INT DEFAULT 18 CHECK(Age >0 AND Age < 100),
FirstName NVARCHAR(20) NOT NULL,
LastName NVARCHAR(20) NOT NULL,
Email VARCHAR(30) UNIQUE CHECK(Email !=''),
Phone VARCHAR(20) UNIQUE CHECK(Phone !='')
);

Shuningdek, u "Elektron pochta" va "Telefon" ustunlarida qiymat sifatida bo'sh satr bo'lishi mumkin emasligini bildiradi (bo'sh satr NULLga teng emas).

AND kalit so`zi shartlarni birlashtirish uchun ishlatiladi. Shartlar (>) dan katta, (<) dan kam, teng bo'lmagan (!=) taqqoslash operasiyalari sifatida ko`rsatilishi mumkin.
Bundan tashqari, CHECK-dan foydalanib, jadval uchun umumiy cheklov yaratishingiz mumkin:
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,
CHECK((Age >0 AND Age<100) AND (Email !='') AND (Phone !=''))
)

CONSTRAINT operatori. Cheklovlar nomini belgilash.

CONSTRAINT kalit so`zidan cheklovlar nomini ko`rsatish uchun foydalanish mumkin. PRIMARY KEY, UNIQUE, DEFAULT, CHECK cheklov sifatida ishlatilishi mumkin.
Cheklov nomlari ustun darajasida ko`rsatilishi mumkin. Ular atributlardan oldin CONSTRAINTdan keyin ko`rsatilgan: CREATE TABLE Customers
(
Id INT CONSTRAINT PK_Customer_Id PRIMARY KEY IDENTITY,
Age INT
CONSTRAINT DF_Customer_Age DEFAULT 18
CONSTRAINT CK_Customer_Age CHECK(Age >0 AND Age < 100),
FirstName NVARCHAR(20) NOT NULL,
LastName NVARCHAR(20) NOT NULL,
Email VARCHAR(30) CONSTRAINT UQ_Customer_Email UNIQUE,
Phone VARCHAR(20) CONSTRAINT UQ_Customer_Phone UNIQUE
)