SELECT Customers.CName, SalepeopIe.SName, Salepeople.City FROM Salepeople, CustomersSELECT Customers.CName, SalepeopIe.SName FROM Customers, Salepeople W HERE Salepeople.SNum=Customers.SNum;JchkiSELECT book, title, author, name FROM author, book WHERE book.author = author .id;SELECT book.title, author.name FROM author LEFT |
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| bet | 32/71 | | Sana | 28.05.2024 | | Hajmi | 24,2 Mb. | | #255852 |
Bog'liq Ma\'lumotlar bazasi. ZaynidinovX.N.Bu sahifa navigatsiya:
- SELECT Customers.CName, SalepeopIe.SName, Salepeople.City FROM Salepeople, Customers
- SELECT Customers.CName, SalepeopIe.SName FROM Customers, Salepeople W HERE Salepeople.SNum=Customers.SNum;
- Jchki
- SELECT book, title, author, name FROM author, book WHERE book.author = author .id;
- SELECT book.title, author.name FROM author LEFT
SELECT Customers.*, Salepeople.* FROM Salepeople, Customers;
Lekin bu verda hosil b o ‘lgan jadval keraksiz m a’lnmotlarga ega. Keraksiz satrlami olib tashlash uchun W HERE jumlasidan foydalaniladi.
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Masalan: berilgan shahardagi sotuvchilar va buyurtmachilar ixtiyoriy kombinatsiyasini ko‘rish uchun quyidagini kiritish lozim:
SELECT Customers.CName, SalepeopIe.SName, Salepeople.City FROM Salepeople, Customers W H ER E Salepeople.City = Customers.City;
Jamlashda SQL bir necha jadval satrlari kombinatsiyasini predikatlar b o ‘yicha solishtirishdir. Asosan m a’lumotlar ilovaii yaxlitlik asosida tekshirilib, ajratib olinadi.
Misol: har bir sotuvchiga mos keluvchi buyurtmachilar ro'yxati:
SELECT Customers.CName, SalepeopIe.SName FROM Customers, Salepeople W HERE Salepeople.SNum=Customers.SNum;
Tenglikka asoslangan predikatlardan foydalanuvchi jamlanmalar, tenglik bo‘yicha jamlanma deb atalib, jamlanmalammg eng umumiy ko'rinishidir. Shu bilan birga ixtiyoriy relyatsion operatordan foydalanish mumkin.
Jchki va tashqijamlashlar
jam lashlar bir jadval satriga ikkinchi jadval satrlarini mos qo'yishga imkon beradi. Jamlashlar asosiy turi bu ichki jamlashdir. Jadvallarni ichki jam lash ikki jadval usutunlarini tenglashtirishga asoslangandir:
SELECT book, title, author, name FROM author, book WHERE book.author = author .id;
MySQL jamlashning kuchliroq tipi ya'ni chap tashqi jam lash (yoki tashqi jam lashjdan foydalanishga imkon beradi. Jamlashni bu tunning ichki jam lashdan farqi shundaki natijaga o‘ng jadvalda mos ustunga ega bo'lmagan chap jadval ustunlari qo'shiladi. Agar avtorlar va kitoblar misoliga e’tibor bersangiz natijaga m a’lumotlar bazasida ldtoblarga ega boim agan kitoblar kirmagan edi.
K o'p hollarda o'ng jadvalda m osi bo‘lmagan chap jadvaldagi satrlarni chiqarish kerak bo'ladi. Bunt tashqi jam lash yordamida amalga oshirish mumkin:
o3
SELECT book.title, author.name FROM author LEFT JO IN
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