المعاملات المنطقية في SQL (Logical Operators)

SELECT column1, column2
FROM table_name
WHERE condition1 AND condition2;

+----+-----------+-----+--------+--------+
| id | name      | age | city   | grade  |
+----+-----------+-----+--------+--------+
| 1  | أحمد      | 20  | الرياض | A      |
| 2  | فاطمة     | 19  | جدة    | B      |
| 3  | محمد      | 21  | الرياض | A      |
| 4  | سارة      | 20  | مكة    | C      |
| 5  | علي       | 22  | جدة    | B      |
| 6  | نورة      | 19  | الرياض | A      |
+----+-----------+-----+--------+--------+

SELECT name, age, city FROM students
WHERE city = 'الرياض' AND age = 20;

+-----------+-----+--------+
| name      | age | city   |
+-----------+-----+--------+
| أحمد      | 20  | الرياض | ✓ (الرياض ✓ AND 20 ✓)
+-----------+-----+--------+
1 row in set

-- لماذا لم تظهر نورة؟
-- نورة: الرياض ✓ لكن عمرها 19 ✗ → FALSE
-- محمد: الرياض ✓ لكن عمره 21 ✗ → FALSE

SELECT name, city, grade FROM students
WHERE city = 'الرياض' AND grade = 'A';

+-----------+--------+--------+
| name      | city   | grade  |
+-----------+--------+--------+
| أحمد      | الرياض | A      | ✓
| محمد      | الرياض | A      | ✓
| نورة      | الرياض | A      | ✓
+-----------+--------+--------+
3 rows in set

SELECT name, age, city, grade FROM students
WHERE city = 'الرياض' AND grade = 'A' AND age >= 20;

+-----------+-----+--------+--------+
| name      | age | city   | grade  |
+-----------+-----+--------+--------+
| أحمد      | 20  | الرياض | A      | ✓ (الرياض ✓ AND A ✓ AND 20 ✓)
| محمد      | 21  | الرياض | A      | ✓ (الرياض ✓ AND A ✓ AND 21 ✓)
+-----------+-----+--------+--------+
2 rows in set

-- نورة لم تظهر لأن عمرها 19 (أقل من 20)

SELECT name, city FROM students
WHERE city = 'الرياض' OR city = 'جدة';

+-----------+--------+
| name      | city   |
+-----------+--------+
| أحمد      | الرياض | ✓ (الرياض = TRUE)
| فاطمة     | جدة    | ✓ (جدة = TRUE)
| محمد      | الرياض | ✓ (الرياض = TRUE)
| علي       | جدة    | ✓ (جدة = TRUE)
| نورة      | الرياض | ✓ (الرياض = TRUE)
+-----------+--------+
5 rows in set

-- سارة لم تظهر لأنها من مكة (لا الرياض ولا جدة)

SELECT name, age, grade FROM students
WHERE age < 20 OR grade = 'A';

+-----------+-----+--------+
| name      | age | grade  |
+-----------+-----+--------+
| أحمد      | 20  | A      | ✓ (grade = A)
| فاطمة     | 19  | B      | ✓ (age < 20)
| محمد      | 21  | A      | ✓ (grade = A)
| نورة      | 19  | A      | ✓ (age < 20 OR grade = A)
+-----------+-----+--------+
4 rows in set

SELECT name, city FROM students
WHERE NOT city = 'الرياض';

+-----------+--------+
| name      | city   |
+-----------+--------+
| فاطمة     | جدة    |
| سارة      | مكة    |
| علي       | جدة    |
+-----------+--------+
3 rows in set

SELECT name, age, grade FROM students
WHERE NOT (age < 20 OR grade = 'C');

+-----------+-----+--------+
| name      | age | grade  |
+-----------+-----+--------+
| أحمد      | 20  | A      | ✓ (NOT (FALSE OR FALSE) = TRUE)
| محمد      | 21  | A      | ✓
| علي       | 22  | B      | ✓
+-----------+-----+--------+
3 rows in set

SELECT name, city, grade FROM students
WHERE city = 'الرياض' OR city = 'جدة' AND grade = 'A';

-- كيف يُقرأ هذا؟
-- (city = 'الرياض') OR ((city = 'جدة') AND (grade = 'A'))
-- AND يُقيّم أولاً!

-- الطريقة 1: طلاب متفوقون من الرياض أو جدة
SELECT name, city, grade FROM students
WHERE (city = 'الرياض' OR city = 'جدة') AND grade = 'A';

-- النتيجة: أحمد، محمد، نورة (من الرياض بدرجة A فقط)
-- فاطمة وعلي لن يظهروا لأن درجتهم B

+-----------+--------+--------+
| name      | city   | grade  |
+-----------+--------+--------+
| أحمد      | الرياض | A      | ✓
| محمد      | الرياض | A      | ✓
| نورة      | الرياض | A      | ✓
+-----------+--------+--------+
3 rows in set

+----+------------------+--------+-------+----------+
| id | name             | price  | stock | category |
+----+------------------+--------+-------+----------+
| 1  | لابتوب Dell      | 3500   | 15    | الكترونيات |
| 2  | ماوس لاسلكي      | 50     | 200   | اكسسوارات |
| 3  | شاشة Samsung     | 800    | 25    | الكترونيات |
| 4  | كاميرا Canon     | 2500   | 5     | تصوير    |
+----+------------------+--------+-------+----------+

SELECT name, price, stock FROM products
WHERE price > 1000 OR stock < 10;

+------------------+--------+-------+
| name             | price  | stock |
+------------------+--------+-------+
| لابتوب Dell      | 3500   | 15    | ✓ (price > 1000)
| كاميرا Canon     | 2500   | 5     | ✓ (price > 1000 AND stock < 10)
+------------------+--------+-------+

SELECT name, department, salary FROM employees
WHERE (department = 'IT' OR department = 'Sales') 
  AND salary >= 7000;

SELECT name, category FROM products
WHERE NOT (category = 'الكترونيات' OR category = 'اكسسوارات');

-- سيء: غامض
WHERE a = 1 OR b = 2 AND c = 3

-- جيد: واضح
WHERE (a = 1 OR b = 2) AND c = 3
-- أو
WHERE a = 1 OR (b = 2 AND c = 3)

-- سيء: متكرر
WHERE city = 'الرياض' OR city = 'جدة' OR city = 'مكة'

-- جيد: أقصر وأوضح (سنتعلمها لاحقاً)
WHERE city IN ('الرياض', 'جدة', 'مكة')