SQL SELECT DISTINCT

SQL SELECT DISTINCT buyrug‘i

SELECT DISTINCT buyrug‘i faqat alohida (UNIQUE) qiymatlarni qaytarish uchun ishlatiladi.

Jadvaldagi ustun bir nechta takroriy qiymatlarga ega bo‘lishi mumkin - ba’zan esa faqat noyob (turli) qiymatlarni chiqarish kerak bo‘ladi.

"Customers" jadvalidagi barcha turli (takrorlanmaydigan) mamlakatlarni tanlang:

SELECT DISTINCT Country FROM Customers;

SELECT DISTINCT column1, column2, ... FROM table_name;

Quyida misollarda foydalanilgan Customers jadvalidan tanlanma 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
4	Around the Horn	Thomas Hardy	120 Hanover Sq.	London	WA1 1DP	UK
5	Berglunds snabbköp	Christina Berglund	Berguvsvägen 8	Luleå	S-958 22	Sweden

Agar siz DISTINCT kalit so‘zini tushirib qoldirsangiz, SQL buyrug‘i "Customers" jadvalidagi barcha yozuvlarning "Country" qiymatini qaytaradi:

SELECT Country FROM Customers;

DISTINCT kalit so‘zi bilan COUNT() funksiyasidan foydalanib, noyob mamlakatlar sonini sanashimiz mumkin.

SELECT COUNT(DISTINCT Country) FROM Customers;

Eslatma: COUNT(DISTINCT ustun_nomi) IN Microsoft Access ma’lumotlar bazalarida qo‘llab-quvvatlanmaydi.

Mana MS Access uchun muqobil yechim:

SELECT Count(*) AS DistinctCountries
FROM (SELECT DISTINCT Country FROM Customers);

COUNT() funksiyasi haqida ushbu darslikda keyinroq bilib olasiz.

Yutuqlaringizni kuzating – bu bepul!