MYSQL Left Join with Subquery

Question

I am trying to pull the inventory and convert all items to pounds, and then left join my dough recipes and also convert the dough recipes to a base unit of pounds. Eventually I will be running a calculation within the query on inventory_pounds and dough_recipe_ingredient_pounds so they need to remain as sub-queries I believe. I cannot figure out why this query will not work. Any suggestions or rationale?

The error I see is: #1054 - Unknown column 'dough_recipes.inventory_id' in 'on clause'

SELECT inventory.id, inventory.title,
(SELECT 
CASE inventory.units
WHEN  'kilograms'
THEN 2.20462 * inventory.quantity
WHEN  'pounds'
THEN 1 * inventory.quantity
WHEN  'ounces'
THEN 0.0625 * inventory.quantity
WHEN  'grams'
THEN 0.00220462 * inventory.quantity
END ) as inventory_pounds

FROM inventory

LEFT JOIN  
(SELECT 
CASE dough_recipes.units
WHEN 'kilograms'
THEN 2.20462 * dough_recipes.amount
WHEN 'pounds'
THEN 1 * dough_recipes.amount
WHEN 'ounces'
THEN 0.0625 * dough_recipes.amount
WHEN 'grams'
THEN 0.00220462 * dough_recipes.amount
END  FROM dough_recipes ) AS dough_recipe_ingredient_pounds ON inventory.id =        
dough_recipes.inventory_id

---

UPDATE: I got the entire query to work....but the variable return AS are not working in calculations like I was thinking they would. Is there a way to get them to work?

SELECT inventory.id, inventory.title,
(SELECT 
CASE inventory.units
WHEN  'kilograms'
THEN 2.20462 * inventory.quantity
WHEN  'pounds'
THEN 1 * inventory.quantity 
WHEN  'ounces'
THEN 0.0625 * inventory.quantity
WHEN  'grams'
THEN 0.00220462 * inventory.quantity
END ) as inventory_pounds,
(SELECT 
CASE dough_recipes.units
WHEN 'kilograms'
THEN 2.20462 * dough_recipes.amount
WHEN 'pounds'
THEN 1 * dough_recipes.amount
WHEN 'ounces'
THEN 0.0625 * dough_recipes.amount
WHEN 'grams'
THEN 0.00220462 * dough_recipes.amount
END ) AS dough_recipe_ingredient_pounds,products.units,(orders_items.quantity -     
orders_items.quantity_baked) AS num_loaved_needed,
( SELECT CASE doughs.units
WHEN 'kilograms'
THEN 2.20462 * doughs.yield
WHEN 'pounds'
THEN 1 * doughs.yield
WHEN 'ounces'
THEN 0.0625 * doughs.yield
WHEN 'grams'
THEN 0.00220462 * doughs.yield
END )
AS dough_recipe_yield_pounds
FROM inventory
LEFT JOIN  dough_recipes ON inventory.id = dough_recipes.inventory_id
LEFT JOIN products ON dough_recipes.dough_id = products.dough_id
LEFT JOIN orders_items ON products.id = orders_items.product_id
LEFT JOIN doughs ON doughs.id = products.dough_id

This is the calculation the is not working when added to the query:

dough_recipe_ingredient_pounds / dough_recipe_yield_pounds * products.weight *     
(orders_items.quantity - orders_items.quantity_baked) AS   
amount_needed_for_all_current_orders

Answer 1

The second part of your query is creating a temporary table named dough_recipe_ingredient_pounds and trying to join it with inventory. This second table does not have inventory_id which is why you are getting the error. Your query should be:

SELECT inventory.id, inventory.title,
(SELECT 
CASE inventory.units
WHEN  'kilograms'
THEN 2.20462 * inventory.quantity
WHEN  'pounds'
THEN 1 * inventory.quantity
WHEN  'ounces'
THEN 0.0625 * inventory.quantity
WHEN  'grams'
THEN 0.00220462 * inventory.quantity
END ) as inventory_pounds,
(SELECT 
CASE dough_recipes.units
WHEN 'kilograms'
THEN 2.20462 * dough_recipes.amount
WHEN 'pounds'
THEN 1 * dough_recipes.amount
WHEN 'ounces'
THEN 0.0625 * dough_recipes.amount
WHEN 'grams'
THEN 0.00220462 * dough_recipes.amount
END  FROM dough_recipes ) AS dough_recipe_ingredient_pounds

FROM inventory

LEFT JOIN  dough_recipes

ON inventory.id = dough_recipes.inventory_id

Answer 2

The engine complains because the last ON is referring dough_recipes , which is not visible at the outer level.

Change the last part to

...
LEFT JOIN  
(SELECT inventory_id, 
 CASE dough_recipes.units
  WHEN 'kilograms'
  THEN 2.20462 * dough_recipes.amount
  WHEN 'pounds'
  THEN 1 * dough_recipes.amount
  WHEN 'ounces'
  THEN 0.0625 * dough_recipes.amount
  WHEN 'grams'
  THEN 0.00220462 * dough_recipes.amount
  END  FROM dough_recipes ) AS dough_recipe_ingredient_pounds 
  ON inventory.id = dough_recipe_ingredient_pounds.inventory_id