PostgreSQL INNER JOIN
ICHKI QO‘SHILMA
INNER JOIN kalit so‘zi ikkala jadvaldagi qiymatlarga mos keladigan yozuvlarni tanlaydi.
Keling, soxta sinov mahsulotlari jadvalimizdan foydalangan holda misolni ko‘rib chiqaylik:
testproduct_id | product_name
| category_id
----------------+------------------------+-------------
1 | Johns Fruit Cake |
3
2 | Marys Healthy Mix |
9
3 | Peters Scary Stuff |
10
4 | Jims Secret Recipe |
11
5 | Elisabeths Best Apples |
12
6 | Janes Favorite Cheese |
4
7 | Billys Home Made Pizza |
13
8 | Ellas Special Salmon |
8
9 | Roberts Rich Spaghetti |
5
10 |
Mias Popular Ice |
14
(10 rows)
Biz toifalar jadvali bilan sinov mahsulotlari jadvaliga qo‘shilishga harakat qilamiz:
category_id | category_name |
description
-------------+----------------+------------------------------------------------------------
1 | Beverages | Soft drinks, coffees, teas,
beers, and ales
2 | Condiments | Sweet and savory sauces, relishes,
spreads, and seasonings
3 | Confections | Desserts, candies, and sweet breads
4 | Dairy Products | Cheeses
5 | Grains/Cereals | Breads, crackers, pasta, and cereal
6 | Meat/Poultry | Prepared meats
7 | Produce | Dried fruit and bean
curd
8 |
Seafood | Seaweed and fish
(8
rows)
E’tibor bering, test mahsulotlaridagi ko‘pgina mahsulotlarda kategoriyalar jadvalidagi toifalarning hech biriga mos kelmaydigan kategoriya_id mavjud.
INNER JOIN-dan foydalanib, biz mos kelmaydigan yozuvlarni olmaymiz, faqat ikkala jadvalga mos keladigan yozuvlarni olamiz:
Misol
Kategoriya_id ustunidan foydalanib, test mahsulotlarini toifalarga qo‘shing:
SELECT
testproduct_id, product_name, category_name
FROM testproducts
INNER JOIN categories ON
testproducts.category_id = categories.category_id;
Misolni ishga tushirish »
Natija
Faqat ikkala jadvaldagi mos yozuvlar qaytariladi:
testproduct_id | product_name
| category_name
----------------+------------------------+----------------
1 | Johns Fruit Cake | Confections
6 | Janes Favorite Cheese | Dairy Products
8 | Ellas Special Salmon | Seafood
9 | Roberts Rich Spaghetti | Grains/Cereals
(4 rows)
Eslatma: JOIN va INNER JOIN bir xil natija beradi.
INNER JOIN — JOIN uchun standart birlashma turi, shuning uchun JOIN yozganingizda tahlilchi aslida INNER JOIN deb yozadi.
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