Indexed item from 2 tables into one column - mysql

Question

I want to restrict one column in `orders` MySQL table to primary key from **2 different tables**.
Example:
I have one table orders
|order_id|item_1 |item_2 |price|
|1 |service_id1|product_id1|10.00|
|2 |product_id1|service_id1|10.00|
Columns item_1 and item_2 are basic indexes and I want to restrict each of them to following tables:
services
|service_id |name |price|
|service_id1|service1|5.00 |
|service_id2|service2|5.00 |
products
|product_id |name |price|
|product_id1|product1|5.00 |
|product_id2|product2|5.00 |
Basically i just want to insert data from both services and products into one column: orders.item_1 or orders.item_2. Is it possible? I added both name restrictions in phpmyadmin but it doesn't work like it suppose to work, generating error 1452. Maybe I'm overthinking and the solution is easier than I think or I just want too much from mysql.

Answer 1

This is only a foreign key constraint
Joining both in a single column makes no sense, but is doable
what you essentially have is a bridge taböe, to join different ids from different tables. As the ids are indexed this is ver fast, especially when you are looking for few items .
in the sample you need to have in both tables a 1 to add to orders a 1 as reference, and so you always must have products and services in sync with each other
CREATE tABLE products (product_id bigint Primary KEY auto_increment, name VARCHAR(255),price DECIMAL (10,2))
CREATE tABLE services (sercvice_id bigint Primary KEY auto_increment, name VARCHAR(255),price DECIMAL (10,2))
CREATE TABLe orders (order_id BIGINT AUTO_INCREMENT PRIMARY KEY
,item_1 BIGINT
, item_2 BIGINT
, price DECIMAL(10,2)
,
CONSTRAINT FK_OrdersProducts FOREIGN KEY (item_1)
REFERENCES products(product_id),
CONSTRAINT FK_OrdersServices FOREIGN KEY (item_2)
REFERENCES services(sercvice_id)
, INDEX (item_1,item_2)
)
db<>fiddle here
CREATE tABLE products (product_id bigint Primary KEY auto_increment, name VARCHAR(255),price DECIMAL (10,2))
CREATE tABLE services (sercvice_id bigint Primary KEY auto_increment, name VARCHAR(255),price DECIMAL (10,2))
CREATE TABLe orders (order_id BIGINT AUTO_INCREMENT PRIMARY KEY
,item_1 BIGINT
, price DECIMAL(10,2)
,
CONSTRAINT FK_OrdersProducts FOREIGN KEY (item_1)
REFERENCES products(product_id),
CONSTRAINT FK_OrdersServices FOREIGN KEY (item_1)
REFERENCES services(sercvice_id)
)
db<>fiddle here