SQL asoslari: SELECT, FROM, WHERE

SQL — Structured Query Language — ma'lumotlar bazasi bilan ishlashning asosiy tili.

Birinchi so'rov

-- Barcha ustunlarni tanlash
SELECT * FROM talabalar;

-- Faqat kerakli ustunlar
SELECT ism, yosh, ball FROM talabalar;

-- Alias (taxallus) qo'shish
SELECT ism AS "Talaba ismi", ball AS "Yakuniy ball"
FROM talabalar;

WHERE - Filtrlash

-- Oddiy shart
SELECT * FROM talabalar WHERE yosh > 20;

-- Bir necha shart
SELECT * FROM talabalar
WHERE yosh > 20 AND ball >= 80;

-- YOKI sharti
SELECT * FROM talabalar
WHERE shahar = 'Toshkent' OR shahar = 'Samarqand';

-- Matnni izlash
SELECT * FROM talabalar WHERE ism LIKE 'A%';   -- A bilan boshlanuvchi
SELECT * FROM talabalar WHERE ism LIKE '%ali';  -- ali bilan tugaydigan
SELECT * FROM talabalar WHERE ism LIKE '%ar%';  -- ar ni o'z ichiga olgan

ORDER BY - Tartiblash

-- O'sish tartibida
SELECT * FROM talabalar ORDER BY ball ASC;

-- Kamayish tartibida
SELECT * FROM talabalar ORDER BY ball DESC;

-- Bir necha ustun bo'yicha
SELECT * FROM talabalar
ORDER BY shahar ASC, ball DESC;

LIMIT - Natijalar sonini cheklash

-- Faqat 10 ta
SELECT * FROM talabalar LIMIT 10;

-- 11-20 qatorlar
SELECT * FROM talabalar LIMIT 10 OFFSET 10;

-- Eng yuqori 5 ball
SELECT ism, ball FROM talabalar
ORDER BY ball DESC LIMIT 5;

IN va BETWEEN

-- Ro'yxatdan birida bo'lsa
SELECT * FROM talabalar
WHERE shahar IN ('Toshkent', 'Samarqand', 'Buxoro');

-- Oraliqda bo'lsa
SELECT * FROM talabalar WHERE ball BETWEEN 70 AND 90;

-- NULL tekshirish
SELECT * FROM talabalar WHERE telefon IS NULL;
SELECT * FROM talabalar WHERE telefon IS NOT NULL;