MYSQL左联接与子查询

Question

我试图拉库存，并将所有项目转换为磅，然后加入我的面团配方，还将面团配方转换为磅的基本单位。 最终，我将在查询中对stocking_pounds和dough_recipe_ingredient_pounds进行计算，因此我需要将它们保留为子查询。 我无法弄清楚为什么这个查询将不起作用。 有什么建议或理由吗？

我看到的错误是：＃1054-'on子句'中的未知列'dough_recipes.inventory_id'

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

---

更新：我让整个查询都可以工作....但是变量return AS在计算中不起作用，就像我认为的那样。 有没有办法让他们工作？

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

这是添加到查询中时不起作用的计算：

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

查询的第二部分是创建一个名为oughing_recipe_ingredient_pounds的临时表，然后尝试将其与清单连接。 第二个表没有库存编号，这就是您收到错误的原因。 您的查询应为：

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

引擎抱怨，因为最后一个ON引用的是dough_recipes ，这在外部级别不可见。

将最后一部分更改为

...
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