具有多个表的简单SQL查询

Question

I'm trying to write a simple query but the output is not correct:

Herer my code:

SELECT oc_order_product.order_id AS ordernumber, oc_order_product.quantity,
       oc_order_product.model, oc_order_product.name,
       oc_order.shipping_company, oc_order.shipping_firstname,
       oc_order.shipping_lastname, oc_order.shipping_city, oc_product.location
FROM oc_order_product,
     oc_order,
     oc_product
WHERE oc_order.order_id = oc_order_product.order_id
  AND oc_order.order_status_id = 1
  AND oc_product.location = 1
ORDER BY ordernumber, oc_order_product.model

The output is a list of all products with the oc_order.order_status_id = 1 but the second AND (oc_product.location = 1) is not applied. What is wrong? I don't work with JOIN because I don't understand it really good.

Answer 1

Now using modern, explicit JOIN :

SELECT oc_order_product.order_id AS ordernumber, oc_order_product.quantity,
       oc_order_product.model, oc_order_product.name,
       oc_order.shipping_company, oc_order.shipping_firstname,
       oc_order.shipping_lastname, oc_order.shipping_city, oc_product.location
FROM oc_order_product
    INNER JOIN oc_order ON oc_order.order_id = oc_order_product.order_id
    INNER JOIN oc_product ON oc_product.id = oc_order_product.product_id
WHERE oc_order.order_status_id = 1
  AND oc_product.location = 1
ORDER BY ordernumber, oc_order_product.model

That last join

INNER JOIN oc_product ON oc_product.id = oc_order_product.product_id

is just a guess, since I don't know which columns to use!

Answer 2

jarlh is guessing that oc_product.id = oc_order_product.product_id .

I'm going to guess that your data element names are consistently and uniquely named throughout your schema and therefore suggest you use ultra-modern NATURAL JOIN :

  SELECT order_id AS ordernumber, quantity,
         model, name, shipping_company, shipping_firstname,
         shipping_lastname, shipping_city, location
    FROM oc_order_product
         NATURAL JOIN oc_order
         NATURAL JOIN oc_product
   WHERE order_status_id = 1
         AND location = 1
   ORDER 
      BY ordernumber, model;

...not betting the farm on it, though.