MySql LEFT连接多个具有相同ID或名称的表

Question

i'm having some problems. with the JEFT JOIN sql statement. i have 3 tables:

user , products, prod_images.

table.user user_id 

table.products user_id item_id

table.prod_images user_id item_id

when i run this query to get data that relation, its work fine. but only work if the prod_images table are not empty. when the prod_images empty the sql right join merge the result and i get null to the products.item_id array

 SELECT products.*, prod_images.*, users.*
 FROM products 
 LEFT JOIN prod_images 
    ON products.item_id=prod_images.item_id
    AND prod_images.is_primary = '1'
JOIN users 
    ON users.user_id=products.seller_id 
    WHERE products.status = '1' 
    ORDER BY created DESC 

How can i make this query work fine when the table.prod_images is empty ?

Answer 1

I believe your query is almost ok.

And it returns everything you asked for, but you should avoid of requesting products.*, prod_images.*, users.* because it is easy to confuse ourselves.

So if you change this part at least to SELECT products.item_id PRODUCTS_ITEM_ID, products.*, prod_images.*, users.*

And one another note, your query probably returns no products.item_id not when prod_images has no related records (because it LEFT JOIN ed) but when users has no related records because it is INNER JOIN ed. So I would start from changing JOIN users to LEFT JOIN users .

PS Look at @Reno comment. I did not mention that. for sure you should change ON products.item_id=products.item_id to ON products.item_id=prod_images.item_id