FOREIGN KEY
FOREIGN KEY
FOREIGN KEY cheklovi ikkita jadvalni bir-biriga ulash uchun ishlatiladigan kalitdir.
FOREIGN KEY - bu bir jadvaldagi boshqa jadvalning PRIMARY KEY’iga ishora qiluvchi maydon (yoki maydonlar to‘plami).
SQL FOREIGN KEY on CREATE TABLE
Quyidagi SQL "Orders" jadvali yaratilayotganda "PersonID" ustunida FOREIGN KEY yaratadi:
MySQL:
CREATE TABLE Orders
(
OrderID int NOT NULL,
OrderNumber int NOT NULL,
PersonID int,
PRIMARY KEY (OrderID),
FOREIGN KEY (PersonID) REFERENCES Persons(PersonID)
);SQL Server / Oracle / MS Access:
CREATE TABLE Orders
(
OrderID int NOT NULL PRIMARY KEY,
OrderNumber int NOT NULL,
PersonID int FOREIGN KEY REFERENCES Persons(PersonID)
);FOREIGN KEY cheklovini nomlashga ruxsat berish va bir nechta ustunlarda FOREIGN KEY cheklovini aniqlash uchun quyidagi SQL sintaksisidan foydalaning:
MySQL / SQL Server / Oracle / MS Access:
CREATE TABLE Orders
(
OrderID int NOT NULL,
OrderNumber int NOT NULL,
PersonID int,
PRIMARY KEY (OrderID),
CONSTRAINT FK_PersonOrder FOREIGN KEY (PersonID)
REFERENCES Persons(PersonID)
);SQL FOREIGN KEY on ALTER TABLE
"Orders" jadvali allaqachon yaratilgan bo‘lsa, "PersonID" ustunida FOREIGN KEY cheklovini yaratish uchun quyidagi SQL dan foydalaning:
MySQL / SQL Server / Oracle / MS Access:
ALTER TABLE Orders
ADD FOREIGN KEY (PersonID)
REFERENCES Persons(PersonID);FOREIGN KEY cheklovini nomlashga ruxsat berish va bir nechta ustunlarda FOREIGN KEY cheklovini aniqlash uchun quyidagi SQL sintaksisidan foydalaning:
MySQL / SQL Server / Oracle / MS Access:
ALTER TABLE Orders
ADD CONSTRAINT FK_PersonOrder
FOREIGN KEY (PersonID)
REFERENCES Persons(PersonID);FOREIGN KEY cheklovini o‘chirish (DROP)
FOREIGN KEY cheklovini o‘chirish uchun quyidagi SQL’dan foydalaning:
MySQL:
ALTER TABLE Orders
DROP FOREIGN KEY FK_PersonOrder;SQL Server / Oracle / MS Access:
ALTER TABLE Orders
DROP CONSTRAINT FK_PersonOrder;W3Schools Pathfinder
Yutuqlaringizni kuzating – bu bepul!