SQL LEFT JOIN

LEFT JOIN chap jadvaldagi barcha qatorlarni (table1) va o‘ng jadvaldagi (table2) faqat mos keladigan qatorlarni qaytaradi.

Agar o‘ng jadvalda mos kelmasa, o‘ng jadvaldagi ustunlar uchun natija NULL bo‘ladi.

LEFT JOIN va LEFT OUTER JOIN kalit so‘zlari teng – OUTER kalit so‘zi ixtiyoriy.

SQL LEFT JOIN

LEFT JOIN sintaksisi

SELECT column_name(s)
FROM table1
LEFT JOIN table2
ON table1.column_name = table2.column_name;

Eslatma: Sintaksis tegishli ustunga asoslangan ikkita jadvalni birlashtiradi, va ON kalit so‘zi mos keladigan shartni belgilash uchun ishlatiladi.

Demo ma’lumotlar bazasi

Quyida tanlanma "Customers" jadvali keltirilgan:

CustomerID	CustomerName	ContactName	Address	City	PostalCode	Country
1	Alfreds Futterkiste	Maria Anders	Obere Str. 57	Berlin	12209	Germany
2	Ana Trujillo Emparedados y helados	Ana Trujillo	Avda. de la Constitución 2222	México D.F.	05021	Mexico
3	Antonio Moreno Taquería	Antonio Moreno	Mataderos 2312	México D.F.	05023	Mexico

Va "Orders" jadvalidan tanlov:

OrderID	CustomerID	EmployeeID	OrderDate	ShipperID
10308	2	7	1996-09-18	3
10309	37	3	1996-09-19	1
10310	77	8	1996-09-20	2

Bu yerda biz yuqoridagi ikkita jadval orasidagi tegishli ustun "CustomerID" ustuni ekanligini ko‘ramiz.

SQL LEFT JOIN misollari

Quyidagi SQL barcha mijozlarni va ularning buyurtmalarini, shu jumladan hech qanday buyurtma bermagan mijozlarni ham qaytaradi:

Misol

SELECT Customers.CustomerName, Orders.OrderID
FROM Customers
LEFT JOIN Orders ON Customers.CustomerID = Orders.CustomerID
ORDER BY Customers.CustomerName;

O‘zingiz sinab ko‘ring »

Maslahat: Faqat tartib bermagan mijozlarni topish uchun o‘ng jadvaldagi NULL qiymatlarni filtrlash uchun WHERE bandini qo‘shing:

Misol

SELECT Customers.CustomerName, Orders.OrderID
FROM Customers
LEFT JOIN Orders
ON Customers.CustomerID = Orders.CustomerID
WHERE Orders.CustomerID IS NULL;

O‘zingiz sinab ko‘ring »

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