Question

So I have written a query that will grab an order (this is for an ecommerce type site), and from that order id it will get all order items (ecom_order_items), print options (c_print_options) and images (images). The eoi_p_id is currently a foreign key from the images table.

This works fine and the query is:

SELECT
eoi_parentid, eoi_p_id, eoi_po_id, eoi_quantity,
i_id, i_parentid,
po_name, po_price
FROM ecom_order_items, images, c_print_options WHERE eoi_parentid = '1' AND i_id = eoi_p_id AND po_id = eoi_po_id;

The above would grab all the stuff I need for order #1

Now to complicate things I added an extra table (ecom_products), which needs to act in a similar way to the images table. The eoi_p_id can also point at a foreign key in this table too. I have added an extra field ‘eoi_type’ which will either have the value ‘image’, or ‘product’.

Now items in the order could be made up of a mix of items from images or ecom_products. Whatever I try it either ends up with too many records, wont actually output any with eoi_type = ‘product’, and just generally wont work. Any ideas on how to achieve what I am after? Can provide SQL samples if needed?

SELECT
eoi_id, eoi_parentid, eoi_p_id, eoi_po_id, eoi_po_id_2, eoi_quantity, eoi_type,
i_id, i_parentid,
po_name, po_price, po_id,
ep_id
FROM ecom_order_items, images, c_print_options, ecom_products WHERE eoi_parentid = '9' AND i_id = eoi_p_id AND po_id = eoi_po_id

The above outputs duplicate rows and doesnt work as expected. Am I going about this the wrong way? Should I have seperate foreign key fields for the eoi_p_id depending it its an image or a product?

Should I be using JOINs?

Here is a mysql explain of the tables in question

ecom_products

+-------------+--------------+------+-----+---------+----------------+
| Field       | Type         | Null | Key | Default | Extra          |
+-------------+--------------+------+-----+---------+----------------+
| ep_id       | int(8)       | NO   | PRI | NULL    | auto_increment |
| ep_title    | varchar(255) | NO   |     | NULL    |                |
| ep_link     | text         | NO   |     | NULL    |                |
| ep_desc     | text         | NO   |     | NULL    |                |
| ep_imgdrop  | text         | NO   |     | NULL    |                |
| ep_price    | decimal(6,2) | NO   |     | NULL    |                |
| ep_category | varchar(255) | NO   |     | NULL    |                |
| ep_hide     | tinyint(1)   | NO   |     | 0       |                |
| ep_featured | tinyint(1)   | NO   |     | 0       |                |
+-------------+--------------+------+-----+---------+----------------+

ecom_order_items

+--------------+-------------+------+-----+---------+----------------+
| Field        | Type        | Null | Key | Default | Extra          |
+--------------+-------------+------+-----+---------+----------------+
| eoi_id       | int(8)      | NO   | PRI | NULL    | auto_increment |
| eoi_parentid | int(8)      | NO   |     | NULL    |                |
| eoi_type     | varchar(32) | NO   |     | NULL    |                |
| eoi_p_id     | int(8)      | NO   |     | NULL    |                |
| eoi_po_id    | int(8)      | NO   |     | NULL    |                |
| eoi_quantity | int(4)      | NO   |     | NULL    |                |
+--------------+-------------+------+-----+---------+----------------+

c_print_options

+------------+--------------+------+-----+---------+----------------+
| Field      | Type         | Null | Key | Default | Extra          |
+------------+--------------+------+-----+---------+----------------+
| po_id      | int(8)       | NO   | PRI | NULL    | auto_increment |
| po_name    | varchar(255) | NO   |     | NULL    |                |
| po_price   | decimal(6,2) | NO   |     | NULL    |                |
+------------+--------------+------+-----+---------+----------------+

images

+--------------+--------------+------+-----+---------+----------------+
| Field        | Type         | Null | Key | Default | Extra          |
+--------------+--------------+------+-----+---------+----------------+
| i_id         | int(8)       | NO   | PRI | NULL    | auto_increment |
| i_filename   | varchar(255) | NO   |     | NULL    |                |
| i_data       | longtext     | NO   |     | NULL    |                |
| i_parentid   | int(8)       | NO   |     | NULL    |                |
+--------------+--------------+------+-----+---------+----------------+

Answer 1

This is how I’d write the first query. I prefer to use joins.

SELECT eoi_parentid, eoi_p_id, eoi_po_id, eoi_quantity, i_id, i_parentid, po_name, po_price
FROM ecom_order_items
INNER JOIN images
    ON i_id = eoi_p_id
INNER JOIN c_print_options 
    ON po_id = eoi_po_id
WHERE eoi_parentid = '1'

For your second query I would use a UNION on two queries, one for images and one for products.

SELECT eoi_id, eoi_parentid, eoi_p_id, eoi_po_id, eoi_po_id_2, eoi_quantity, eoi_type, i_id, i_parentid, po_name, po_price, po_id, ep_id
FROM ecom_order_items
INNER JOIN images
    ON i_id = eoi_p_id
INNER JOIN c_print_options
    ON po_id = eoi_po_id
WHERE eoi_type = 'image' AND i_id = eoi_p_id --Image conditions
  AND eoi_parentid = '9'   
  AND po_id = eoi_po_id

UNION

SELECT eoi_id, eoi_parentid, eoi_p_id, eoi_po_id, eoi_po_id_2, eoi_quantity, eoi_type, i_id, i_parentid, po_name, po_price, po_id, ep_id
FROM ecom_order_items
INNER JOIN images
    ON i_id = eoi_p_id
INNER JOIN c_print_options
    ON po_id = eoi_po_id
WHERE eoi_type = 'product' AND ep_id = eoi_p_id -- Product conditions
  AND eoi_parentid = '9' 
  AND po_id = eoi_po_id