Question

i already submit my problem but without example it was not clear enough so here is the tables :

Users
id_user / key_user
1       / 123FDADA21312QD
2       / 994GFCS4595433D

Companies
id_company / key_company
1          / 3123123123
2          / 5435345454

Products
id_product / id_company_product / code_product
1          /     1              / iphone
2          /     1              / iBook
3          /     1              / macbook

Tyds
id_tyd  / user_tyd / product_tyd
1       /   1      /   1        -- mean that the id_user = 1 made a line for the iphone 
                                   sold by the company 1
2       /   1      /   2        -- same : user 1 for the ibook of company 1

Here is my request :

SELECT 
products.id_product,
users.id_user,
COALESCE(id_tyd, 'NONE') AS id_tyd 
FROM tyds
INNER JOIN users
ON tyds.user_tyd = users.id_user
INNER JOIN products
ON tyds.product_tyd = products.id_product
INNER JOIN companies
ON products.id_company_product = companies.id_company 
WHERE users.key_user = '123FDADA21312QD'
AND companies.module_key_company = '3123123123'
AND products.cancelled_product >= 0
AND products.code_product = 'iphone'

That will return

products.id_product = 1
users.id_user = 1 
tyds.id_tyd = 1

Perfect. But what i’d like to do is getting the users.id_user EVEN IF there is no records for this user in tyds. Like :

SELECT 
products.id_product,
users.id_user,
COALESCE(id_tyd, 'NONE') AS id_tyd 
FROM tyds
INNER JOIN users
ON tyds.user_tyd = users.id_user
INNER JOIN products
ON tyds.product_tyd = products.id_product
INNER JOIN companies
ON products.id_company_product = companies.id_company 
WHERE users.key_user = '123FDADA21312QD'
AND companies.module_key_company = '3123123123'
AND products.cancelled_product >= 0
AND products.code_product = 'macbook'

I’d like to get :

• products.id_product = 3
• users.id_user = 1
• tyds.id_tyd = NONE

Because at this step, i’m sure that the product i ask exists and the user_key exist. But i’m not sure that there is matching records in tyds and that is what i want to test.

Of course, all the tables are simplify and i’ll need more datas but i think this will make my point.

My first move was to put the WHERE condition in the JOIN match but, don’t know why, if i put the products.code_product in the products jointure, it give me tyds records even for different id_product…

Thanks a lot for your help !

Answer 1

if that’s the case, change the join from INNER JOIN to LEFT JOIN. INNER JOIN, basically returns rows that are present (atleast one match) on all tables being joined, while LEFT JOIN returns rows on the lefthand side even without matching records on the other tables.

Query,

SELECT c.*, d.id_tyd
FROM
    (
      SELECT  a.id_user, b.id_product
      FROM    users a CROSS JOIN products b
    ) c
    LEFT JOIN tyds d
      ON d.user_tyd = c.id_user AND
         d.product_tyd = c.id_product
    LEFT JOIN products e
      ON e.id_product = c.id_product
    LEFT JOIN companies f
      ON e.id_company_product = f.id_company
    LEFT JOIN users g
      ON c.id_user = g.id_user
WHERE e.code_product = 'macbook' AND
      f.key_company = '3123123123' AND
      g.key_user = '123FDADA21312QD'

• SQLFiddle Demo