Exclude result from MySQL query in JOIN - php

Question

I have multiple tables with orders and deliveries and I want to get only open orders (only those orders that do not have records in delivery table).
So, my tables look like:
Orders table (sh_comenzi):
id partner
1 Partner X
2 Partner Y
3 Partner Z
4 Partner Q
Order lines table (sh_comenzi_pos) where idc is the id of sh_comenzi table
id idc cPos quantity
1 1 1 5
2 1 2 10
3 1 3 20
4 2 1 10
5 2 2 15
6 3 1 10
7 3 2 5
8 3 3 8
9 4 1 15
The deliveries items table is (sh_delivery_items)
id idc cPos
1 1 1
2 1 3
3 2 2
4 3 1
5 3 2
6 3 3
The desired result should give me an output of open orders just like this:
id partner
1 Partner X
2 Partner Y
4 Partner Q
The result doesn't have to keep track o quantities, just on lines level. If one line from orders exists in sh_delivery_items then that line is closed.
I tried something like this:
SELECT DISTINCT sh_comenzi.id, partner FROM sh_comenzi
LEFT JOIN sh_comenzi_pos ON sh_comenzi.id = sh_comenzi_pos.idc
LEFT JOIN sh_delivery_items ON (sh_comenzi_pos.idc = sh_delivery_items.idc AND sh_comenzi_pos.cPos = sh_delivery_items.cPos)
WHERE sh_comenzi.id IS NOT NULL
ORDER BY sh_comenzi.id DESC
Could someone help me?

Answer 1

This is the query you need:
SELECT DISTINCT c.*
FROM sh_comenzi c
INNER JOIN sh_comenzi_pos p
ON c.id = p.idc
LEFT JOIN sh_delivery_items di # 'di' from 'delivery items'
ON p.idc = di.idc AND p.cPos = di.cPos
WHERE di.id IS NULL # keep only not-delivered items
How it works
It combines all the orders (table sh_comenzi) with their line items (table sh_comenzi_pos). The INNER JOIN will leave out the empty orders (if any); if you need them then use LEFT JOIN instead.
Next, each row (order, line item) is combined with the delivery information (table sh_delivery_items) using the pair of columns (idc, cPos). The LEFT JOIN ensures all the rows from the left side table (or result set) appear in the final result set; if a row from the right side table cannot be found to match the row from the left, a row full of NULLs is used instead. This happens for the line items that were not delivered yet (there is no record for them in sh_delivery_items).
Then, the WHERE clause keeps only the rows having NULLs in the di table (sh_delivery_items), i.e. the line items that were not delivered, together with the orders that own them.
Finally, SELECT DISTINCT c.* selects only the columns from the orders table (sh_comenzi) and DISTINCT ensures each order appear only once. Otherwise, each order appears once for each of its line items that was not delivered.
Complete the query yourself with the desired ORDER BY clause.