SQLni qanchalik yaxshi bilasiz?

Senior darajasida SQL bilimlari chuqur tushunishni talab qiladi:

• Asosiy operatsiyalar: SELECT, INSERT, UPDATE, DELETE
• JOIN, subqueries, agregat funksiyalar bilan murakkab so'rovlar
• So'rovlarni optimallashtirish: indekslar, bajarish rejasi, ishlashni tahlil qilish
• Transaktsiyalar va izolyatsiya darajalari
• Ma'lumotlar bazasi protseduralari va triggerlari
• Ma'lumotlarni normalization va denormalization qilish
• Turli ma'lumotlar bazasi tizimlari va ularning xususiyatlari bilan ishlash

Masalan, bir nechta JOIN va agregat funksiyalar bilan optimal so'rov yozishni bilish:

SELECT c.customer_id, c.name, SUM(o.amount) AS total_spent
FROM customers c
JOIN orders o ON c.customer_id = o.customer_id
WHERE o.order_date >= '2023-01-01'
GROUP BY c.customer_id, c.name
HAVING SUM(o.amount) > 1000
ORDER BY total_spent DESC;

Shuningdek, bajarish rejalarini tahlil qilish va so'rovlarni optimallashtirish orqali ishlash samaradorligini oshirish muhimdir.