2-dars. Query data (SELECT)

Ushbu darsda query data (ma’lumotlarni so’rash) ning bir qancha asosiy funksiyalari bilan tanishamiz!

SELECT

SELECT — jadval ichidan ma’lumot olish uchun ishlatiladi.

Misol:

SELECT * FROM users

• SELECT → ma’lumotni tanlash

• * barcha ustunlarni olish

• FROM users → users jadvalidan

Kerakli ustunlarni olish:

SELECT name, age FROM users

FROM

FROM — qaysi jadvaldan ma’lumot olinayotganini ko‘rsatadi.

Misol:

SELECT * FROM products

• products → jadval nomi

• SQL ma’lumotni shu jadvaldan oladi

WHERE

WHERE — ma’lumotlarni filter qilish uchun ishlatiladi.

Misol:

SELECT * FROM users
WHERE age > 18

• WHERE → shart berish

• age > 18 → yoshi 18 dan katta userlarni chiqarish

ORDER BY

ORDER BY — ma’lumotlarni tartiblash uchun ishlatiladi.

Misol:

SELECT * FROM users
ORDER BY age

• ORDER BY age

  → yosh bo‘yicha tartiblaydi

Kichikdan kattaga:

ORDER BY age ASC

• ASC → ascending

• 1 → 100

Kattadan kichikka:

ORDER BY age DESC

• DESC → descending

• 100 → 1

GROUP BY

GROUP BY — bir xil qiymatlarni guruhlash uchun ishlatiladi.

Misol:

SELECT department, COUNT(*)
FROM employees
GROUP BY department

• department → bo‘lim nomi

• COUNT(*) → nechta employee borligini sanaydi

• GROUP BY department

  → bo‘limlar bo‘yicha guruhlaydi

Natija:

HAVING

HAVING — guruhlangan ma’lumotlarga filter qo‘yadi.

Misol:

SELECT department, COUNT(*)
FROM employees
GROUP BY department
HAVING COUNT(*) > 3

• avval group qiladi

• keyin employee soni 3 tadan katta group’larni chiqaradi

WHERE va HAVING farqi:

DISTINCT

DISTINCT — takrorlangan qiymatlarni olib tashlaydi.

Misol:

SELECT DISTINCT city
FROM users

Agar:

• Tashkent

• Tashkent

• Samarkand

bo‘lsa, natijada:

• Tashkent

• Samarkand

chiqadi.

TOP

TOP — yuqoridagi bir nechta qatorni olish uchun ishlatiladi.

Misol:

SELECT TOP 5 *
FROM products

• faqat birinchi 5 ta qatorni chiqaradi

Query Order & Execution

SQL query yozilish tartibi:

SELECT
FROM
WHERE
GROUP BY
HAVING
ORDER BY

Lekin SQL ichida bajarilish tartibi boshqacha:

FROM
WHERE
GROUP BY
HAVING
SELECT
ORDER BY

Darsga tegishli SQL fayllar

⬇️ Darsda ishlatilgan .sql fayli: 📎 2-dars.sql (1.5 KB)

⬇️ Uyga vazifa .sql fayli: 📎 2-dars_uyga_vazifa.sql (3.9 KB)