SELECT asoslari

-- Barcha ustunlar
SELECT * FROM talabalar;

-- Aniq ustunlar
SELECT ism, familiya, shahar FROM talabalar;

SELECT
    ism        AS "Ism",
    familiya   AS "Familiya",
    ortacha_baho AS "O'rtacha baho"
FROM talabalar;

-- AS ni tushirib qoldirish mumkin
SELECT ism "Ism", familiya "Familiya" FROM talabalar;

-- Jadval uchun ham
SELECT t.ism, t.familiya
FROM talabalar AS t;

SELECT
    ism,
    familiya,
    CONCAT(ism, ' ', familiya)                  AS toliq_ism,
    ortacha_baho,
    ROUND(ortacha_baho * 20)                    AS foizda,
    YEAR(CURDATE()) - YEAR(tugilgan_sana)       AS yosh
FROM talabalar;

SELECT
    nomi,
    narx,
    soni,
    narx * soni                     AS jami,
    narx * 0.12                     AS qqs,
    narx * soni * 1.12              AS qqs_bilan,
    ROUND(narx * 0.9)               AS chegirmali
FROM mahsulotlar;

-- Barcha shaharlar (takrorlar bilan)
SELECT shahar FROM talabalar;

-- Noyob shaharlar
SELECT DISTINCT shahar FROM talabalar;

-- Bir nechta ustun bo'yicha noyob juftliklar
SELECT DISTINCT shahar, guruh_id FROM talabalar;

-- Faqat 5 ta qator
SELECT ism, ortacha_baho FROM talabalar LIMIT 5;

-- 10-qatordan boshlab 5 ta (sahifalash uchun)
SELECT ism FROM talabalar LIMIT 5 OFFSET 10;

-- Qisqa yozuv: LIMIT offset, soni
SELECT ism FROM talabalar LIMIT 10, 5;

-- Xavfli: 10 million qator qaytishi mumkin
SELECT * FROM loglar;

-- Xavfsiz
SELECT * FROM loglar LIMIT 100;

-- ISHLAMAYDI: WHERE bajarilganda taxallus hali yo'q
SELECT ortacha_baho * 20 AS foizda
FROM talabalar
WHERE foizda > 80;

-- ISHLAYDI: ORDER BY SELECT dan keyin bajariladi
SELECT ortacha_baho * 20 AS foizda
FROM talabalar
ORDER BY foizda DESC;

-- WHERE da to'liq ifodani takrorlash kerak
SELECT ortacha_baho * 20 AS foizda
FROM talabalar
WHERE ortacha_baho * 20 > 80;

SELECT 2 + 3 AS yigindi;
SELECT NOW() AS hozir;
SELECT CURDATE() AS bugun;
SELECT UPPER('salom') AS katta_harf;
SELECT ROUND(3.14159, 2) AS yaxlitlangan;
SELECT CONCAT('Salom, ', 'Husanboy', '!') AS xabar;

SELECT
    CONCAT(ism, ' ', familiya)              AS talaba,
    shahar,
    ortacha_baho,
    ROUND(ortacha_baho * 20)                AS ball_100,
    CASE
        WHEN ortacha_baho >= 4.5 THEN 'A''lo'
        WHEN ortacha_baho >= 3.5 THEN 'Yaxshi'
        WHEN ortacha_baho >= 3.0 THEN 'Qoniqarli'
        ELSE 'Qoniqarsiz'
    END                                      AS daraja,
    TIMESTAMPDIFF(YEAR, tugilgan_sana, CURDATE()) AS yosh
FROM talabalar
ORDER BY ortacha_baho DESC
LIMIT 5;