How to access outer table in a LEFT OUTER JOIN - mysql

Question

In the query below, I am trying to use the first table in a left outer join. However I am getting an error.
SELECT
products.id,
products_cstm.oem_c,
products.mfr_part_num,
products.description,
products.cost,
products.assigned_user_id,
customfields_oo.ans
FROM products
LEFT OUTER JOIN (SELECT COUNT( q.id ) AS ans
, pq.product_id
FROM products_quotes pq
LEFT JOIN quotes q
ON pq.quote_id = q.id
WHERE q.deleted = 0
AND pq.deleted = 0
AND q.stage <> 4
AND (pq.qty_shipped < pq.product_qty)
AND pq.product_id = products.id
GROUP BY pq.product_id
) AS customfields_oo
ON customfields_oo.product_id = products.id
LEFT JOIN products_cstm
ON products.id = products_cstm.id_c
WHERE products.deleted = 0
ORDER BY ans DESC
When I run the query it gives me the following error:
Error Code : 1054
Unknown column 'products.id' in 'where clause'
It is not allowing first "products" table in left outer join query.

Answer 1

The issue is that customfields_oo is a derived table not a correlated subquery. Thus, you cannot reference the outer table from within the definition of the derived table. In this case, you cannot refer to the outer products table from within the customfields_oo definition. Instead, you must do that filter in the On clause outside the dervied table definition.
Select products.id,
products_cstm.oem_c,
products.mfr_part_num,
products.description,
products.cost,
products.assigned_user_id,
customfields_oo.ans
FROM products
Left Join (
Select pq1.product_id
, Count( q1.id ) As ans
From products_quotes As pq1
Left Join quotes As q1
On pq1.quote_id = q1.id
Where q1.deleted = 0
And pq1.deleted = 0
And q1.stage <> 4
And pq1.qty_shipped < pq1.product_qty
Group By pq1.product_id
) As customfields_oo
On customfields_oo.product_id = products.id
Left Join products_cstm
On products.id = products_cstm.id_c
Where products.deleted = 0
Order By customfields_oo.ans Desc
Now, you have stated in comments that this is too slow because, say products where deleted <> 0 might be evaluated in the derived table. If that is the case, then simply expand the derived table to include the filters on the outer products table.
Select products.id,
products_cstm.oem_c,
products.mfr_part_num,
products.description,
products.cost,
products.assigned_user_id,
customfields_oo.ans
FROM products
Left Join (
Select pq1.product_id
, Count( q1.id ) As ans
From products_quotes As pq1
Join products As p1
On p1.products.id = pq1.product_id
Left Join quotes As q1
On pq1.quote_id = q1.id
Where q1.deleted = 0
And pq1.deleted = 0
And q1.stage <> 4
And pq1.qty_shipped < pq1.product_qty
And p1.deleted = 0
Group By pq1.product_id
) As customfields_oo
On customfields_oo.product_id = products.id
Left Join products_cstm
On products.id = products_cstm.id_c
Where products.deleted = 0
Order By customfields_oo.ans Desc

Answer 2

You do not need to have AND pq.product_id = products.id in the where statement. Because you are LEFT JOINing on that. So I think something like this will work:
AND (pq.qty_shipped < pq.product_qty)
GROUP BY pq.product_id) AS customfields_oo
ON customfields_oo.product_id = products.id
LEFT JOIN products_cstm
ON products.id = products_cstm.id_c
WHERE products.deleted = 0
ORDER BY openorder DESC
EDIT
You do not need to LEFT JOIN on the table you are COUNTing on. You can also do ot like this:
SELECT
.....
(
SELECT
COUNT( q.id )
FROM products_quotes pq
LEFT JOIN quotes q
ON pq.quote_id = q.id
WHERE q.deleted = 0
AND pq.deleted = 0
AND q.stage <> 4
AND (pq.qty_shipped < pq.product_qty)
AND pq.product_id = products.id
) AS ans
FROM products
.....