Data Filtering nima?
Database ichida minglab ma’lumotlar bo‘lishi mumkin. Bizga esa ko‘pincha faqat kerakli qismi kerak bo‘ladi.
Masalan:
faqat yoshi 18 dan katta studentlar
faqat Toshkentdagi mijozlar
faqat narxi 1000 dan katta mahsulotlar
Shu ishni WHERE bajaradi.
WHERE va uning operatorlari
SELECT * FROM Employees
WHERE Salary > 5000;SELECT *→ hamma ustunlarni oladiFROM Employees→ Employees jadvalidanWHERE Salary > 5000→ faqat maoshi 5000 dan katta xodimlarni chiqaradi
Taqqoslash operatorlari
Bular qiymatlarni taqqoslash uchun ishlatiladi.
Operator | Ma’nosi | Namuna |
|---|---|---|
= | teng | SELECT * FROM Students WHERE City = 'Tashkent'; |
!= yoki <> | teng emas | SELECT * FROM Students WHERE City != 'Tashkent'; |
> | katta | SELECT * FROM Products WHERE Price > 1000; |
>= | katta yoki teng | SELECT * FROM Products WHERE Price >= 1000; |
< | kichik | SELECT * FROM Products WHERE Price < 1000; |
<= | kichik yoki teng | SELECT * FROM Products WHERE Price <= 1000; |
Mantiqiy operatorlar
Mantiqiy operatorlar bir nechta shartlarni bog‘laydi.
Operator | Ma’nosi | Namuna |
|---|---|---|
AND | Ikkala shart ham bajarilishi (TRUE) kerak | SELECT * FROM Employees WHERE Salary > 5000 AND Department = 'IT'; |
OR | Kamida bitta shart bajarilishi (TRUE) kerak | SELECT * FROM Employees WHERE Salary > 5000 OR Department = 'IT'; |
NOT | Shartni teskarisi qabul qilinadi | SELECT * FROM Products WHERE NOT Price > 1000; |
Oraliq operatori
Operator | Ma’nosi | Namuna |
|---|---|---|
BETWEEN | Oraliqdagi qiymatlarni olish uchun ishlatiladi | SELECT * FROM Employees WHERE Salary BETWEEN 3000 AND 7000; |
A’zolik operatorlari
Operator | Ma’nosi | Namuna |
|---|---|---|
IN | Bir nechta qiymatlardan birini tekshiradi | SELECT * FROM Students WHERE City IN ('Tashkent' , 'Samarqand' , 'Buxoro'); |
NOT IN | Berilgan qiymatlar ichida bo‘lmaganlarni chiqaradi | SELECT * FROM Students WHERE City NOT IN ('Tashkent' , 'Samarqand'); |
IN yoki NOT IN operatorlari OR funksiyasini qayta-qayta ishlatish oldini oladi.
Qidiruv operatori
Matn ichidan qidirish uchun ishlatiladi.
Operator | Ma’nosi | Namuna | Natija |
|---|---|---|---|
% | Istalgan begilar borligini anglatadi | SELECT * FROM Employees WHERE FirstName LIKE 'A%' | Ismi A harfi bilan boshlanadigan employee’lar chiqadi. |
_ | Bitta belgi borligini anglatadi | SELECT * FROM Students WHERE FirstName LIKE '_li' | Bitta belgidan keyin oxiri "li" bilan tugaydigan ism chiqadi. |
Xulosa
WHERE — SQL’dagi eng muhim mavzulardan biri.
Chunki:
kerakli ma’lumotni topadi
database bilan ishlashni osonlashtiradi
katta datalarni boshqarishga yordam beradi
Data filtering bilmagan odam:
SQL yozolmaydi
analiz qilolmaydi
report tayyorlay olmaydi
Shuning uchun:
Comparison Operators
Logical Operators
BETWEEN
IN
LIKE mavzularini yaxshi tushunish juda muhim.
Darsga tegishli SQL fayllar
⬇️ Darsda ishlatilgan .sql fayli: 📎 dars_5.sql (1.9 KB)
⬇️ Uyga vazifa .sql fayli: 📎 dars_5_uy_ishi.sql (4.3 KB)
