ترتيب عمود واحد أو عدة أعمدة باستخدام ORDER BY

لماذا تحتاجون إلى ORDER BY

الفرز باستخدام عمود واحد

SELECT id, email FROM users ORDER BY created_at;       -- oldest first
SELECT id, email FROM users ORDER BY created_at ASC;
SELECT id, email FROM users ORDER BY created_at DESC;  -- newest first

الفرز باستخدام عدة أعمدة

SELECT first_name, last_name, age
FROM users
ORDER BY last_name ASC, first_name ASC, age DESC;

الفرز باستخدام تعبير

SELECT email, full_name
FROM users
ORDER BY LENGTH(email) DESC, email ASC;

الفرز باستخدام اسم مستعار أو موضع

SELECT id, total * 0.9 AS discounted
FROM orders
ORDER BY discounted DESC;     -- by alias

SELECT id, total
FROM orders
ORDER BY 2 DESC;               -- by position (avoid in code — fragile)

NULLS FIRST / NULLS LAST

-- Default: NULLs LAST when ASC, FIRST when DESC
SELECT * FROM users ORDER BY last_login_at DESC NULLS LAST;
SELECT * FROM users ORDER BY last_login_at ASC  NULLS FIRST;

عمليات الفرز المستقرة وكسر التعادل

SELECT * FROM orders
ORDER BY created_at DESC, id DESC;

ORDER BY والفهارس

-- With index on created_at DESC, this can use the index directly:
SELECT * FROM events ORDER BY created_at DESC LIMIT 100;

استخدام CASE في ORDER BY

-- Show priority orders first:
SELECT * FROM orders
ORDER BY
  CASE status
    WHEN 'urgent'   THEN 0
    WHEN 'normal'   THEN 1
    ELSE 2
  END,
  created_at DESC;

يُنفَّذ ORDER BY بعد WHERE

لا تفرزوا الجداول الضخمة من دون LIMIT

SELECT * FROM events ORDER BY created_at DESC LIMIT 50;

مراجعة

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