PostgreSQL RIGHT JOIN
TO‘G‘RI QO‘SHILING
RIGHT JOIN kalit so‘zi "o‘ng" jadvaldan BARCHA yozuvlarni va "chap" jadvaldan mos yozuvlarni tanlaydi. Natija, agar mos kelmasa, chap tomondan 0 ta yozuv.
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)
Eslatma: Sinov mahsulotlaridagi ko‘pgina mahsulotlarda kategoriyalar jadvalidagi toifalarning hech biriga mos kelmaydigan kategoriya_id mavjud.
RIGHT JOIN-dan foydalanib, biz toifalardagi barcha yozuvlarni, hatto test mahsulotlari jadvalida mos kelmaydiganlarni ham olamiz:
Misol
Kategoriya_id ustunidan foydalanib, test mahsulotlarini toifalarga qo‘shing:
SELECT
testproduct_id, product_name, category_name
FROM testproducts
RIGHT JOIN categories ON testproducts.category_id = categories.category_id;
Misolni ishga tushirish »
Natija
Kategoriyalardagi barcha yozuvlar va faqat sinov mahsulotlaridagi mos yozuvlar:
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
|
| Condiments
|
| Meat/Poultry
|
| Beverages
|
| Produce
(8 rows)
Eslatma: RIGHT JOIN va RIGHT OUTER JOIN bir xil natija beradi.
OUTER - RIGHT JOIN uchun standart birlashma turi, shuning uchun RIGHT JOIN deb yozganingizda, tahlilchi aslida RIGHT OUTER JOIN deb yozadi.
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