2-ma’ruza. Ma’lumotlar bazasiga qo’yiladigan talablar. Rеja: Axborot tizimlari va ma'lumotlar bazasi

p; 3 |
| 23 | 20 | 22 | 21 | 2 |
| 24 | 24 | 21 | 22 | 3 |
+----+----+----+----+---------------------------------------+


Olingan matritsa satrlarining tarkibini olish kriteriyasi tavsifi
SELECT operatorining FROM ro'yxatidagi jadvallardan ma'lumotni tanlash kriteriyasi sifatida, murakkab shart WHERE kalit so'zidan keyin yoziladi va quyidagi shaklga ega:
Oddiy shart
yoki
oddiy shart AND murakkab shart
yoki
oddiy shart OR murakkab shart

Oddiy oddiy shartlar quyidagilar.

Taqqoslash


Jadval_to’liq_nomi @ ustun_to’liq nomi_yoki_konstanta
Namuna mosligi
Ustun_to’liq_nomi [NOT] LIKE namuna

Misol.
11-tugun joylashgan joyning koordinatalarini aniqlash uchun quyidagi operatordan foydalanish mumkin:

SELECT * FROM nodes WHERE id = 11;
+----+--------+--------+
| id | x | y |
+----+--------+--------+
| 11 | -35.00 | -10.00 |
+----+--------+--------+
Misol
Aytaylik, 20 tugunga ega bo'lgan barcha cheklangan elementlarning idlarini ularning uchlaridan biri sifatida aniqlash kerak, masalan ushbu SELECT so'rovi bilan yechilishi mumkin.


SELECT id FROM elements
WHERE n1 = 20 OR n2 = 20 OR n3 = 20;
+----+
| id |
+----+
| 20 |
| 21 |
| 18 |
| 23 |
+----+
SELECT * FROM loadings WHERE value IS NOT NULL;
+------+-----------+------+--------+
| type | direction | node | value |
+------+-----------+------+--------+
| f | y | 27 | -50.00 |
| f | x | 27 | -10.00 |