如何基于一个列将列添加到另一张表？

Question

I have my shop database and I want to join two tables together.

id_order | reference | id_shop_group | id_shop | id_carrier | id_lang | id_customer | id_cart

This the header row of my orders table and below is the header of customers table.

id_customer | id_shop_group | id_shop | id_gender | firstname | lastname 

What I want to do is to join them based on id_customer column. More specifically I want to add all columns of customers except the ones that are already there to orders table based on id_customer . After joining the tables should look like this:

id_order|reference|id_shop_group|id_shop|id_carrier|id_lang|id_customer|id_cart|id_gender|firstname|lastname 

When searching for a solution I found INNER JOIN keyword, but I'm not sure how to use it the way I want.

Answer 1

We don't "Add columns to a table". We, instead, submit SQL to the database that returns the result set that we want. In your case we want to Join the two tables and we can do that using an INNER JOIN on your id_customer field that is common between the two tables. We can turn that into it's own table if you want to hold, permanently, those results. It would look something like

SELECT 
    orders.id_order,
    orders.reference,
    orders.id_shop_group,
    orders.id_shop,
    orders.id_carrier,
    orders.id_lang,
    orders.id_customer,
    orders.id_cart,
    customer.id_gender,
    customer.firstname,
    customer.lastname
FROM orders INNER JOIN customer on orders.id_customer = customer.id_customer;

You can tweak the list of fields to be returned from the joining of these tables to suit your needs.

Answer 2

The fact that id_shop and id_shop_group are in both tables suggests they are part of a composite key. You may need to join using all three shared columns to guarantee unique rows. Otherwise you may retrieve duplicate order rows where the customer belongs to more than one shop.

eg

SELECT
...
FROM orders INNER JOIN customer on orders.id_customer = customer.id_customer 
and orders.id_shop_group = customer.id_shop_group
and orders.id_shop = customer.id_shop