MySQL Join Multiple Tables

Question

Overview: I'm trying to join several tables together to create a text string built from the values of the extracted data. I've reached a point where I have encountered the need to pull the meta_value of the meta_key fields that equal _sku and _price . However, I can't figure out how this is done. Any help pointing me in the right direction is very much appreciated.

Specifics: I want to return a row for each possible product and vehicle configuration by creating a string that is structured like this:

SKU, Year, Make, Model, Engine, Title, Price

I have the correct number of results, but I can't figure out how to get the _price and _sku values from the wp_postmeta table.

Final output should look like this:

2T013-ADU00, 2013, Kia, Optima,   Hybrid, All Weather Floor Mats, 65.60
2T013-ADU00, 2013, Kia, Optima,   SX,     All Weather Floor Mats, 65.60
2T013-ADU00, 2013, Kia, Optima,   EX,     All Weather Floor Mats, 65.60
2T013-ADU00, 2013, Kia, Optima,   LX,     All Weather Floor Mats, 65.60
2T013-ADU00, 2012, Kia, Optima,   LX,     All Weather Floor Mats, 65.60
2T013-ADU00, 2012, Kia, Optima,   EX,     All Weather Floor Mats, 65.60
2T013-ADU00, 2012, Kia, Optima,   SX,     All Weather Floor Mats, 65.60
2T013-ADU00, 2012, Kia, Optima,   Hybrid, All Weather Floor Mats, 65.60
988503W000,  2011, Kia, Sportage, Base,   Wiper Blade,            15.75
988503W000,  2011, Kia, Sportage, EX,     Wiper Blade,            15.75

Here is my PHP :

$sql = "
SELECT filter.filterId as Filter, posts.*, model.ModelName as Model, make.MakeName as Make,   year.Year as Year, engine.EngineName as Engine, meta.*
FROM wp_sFilter filter
JOIN wp_posts posts ON filter.productId = posts.ID 
JOIN wp_sModel model ON filter.modelId  = model.modelId 
JOIN wp_sMake make ON filter.makeId  = make.makeId 
JOIN wp_sYear year ON filter.yearId  = year.yearId 
JOIN wp_sEngine engine ON filter.engineId  = engine.engineId 
JOIN wp_postmeta meta ON filter.productId  = meta.post_id 
WHERE post_status = 'publish' 
AND 
post_type = 'product'
AND
meta_key = '_price' OR '_sku'
";


if(!$result = $db->query($sql)){
    die('There was an error running the query [' . $db->error . ']');
}

while($row = $result->fetch_assoc()){
    echo $row['meta_value'].', '.$row['Year'].', '.$row['Make'].', '.$row['Model'].' '.$row['Engine'].', '.$row['post_title'].', '.$row['meta_value'] . '<br />';
}

And here's the mysql tables :

wp_posts

ID | post_status | post_type | post_title
---+-------------------------------------------------
9  | published   | product   | All Weather Floor Mats
11 | published   | product   | Wiper Blade

wp_sFilter

filterId | productId | makeId | modelId | yearId | engineID
---------+-----------+--------+---------+--------+---------
8        | 9         | 1      | 1       | 3      | 12
7        | 9         | 1      | 1       | 3      | 17
6        | 9         | 1      | 1       | 3      | 11
5        | 9         | 1      | 1       | 3      | 10
9        | 9         | 1      | 1       | 2      | 5
10       | 9         | 1      | 1       | 2      | 6
11       | 9         | 1      | 1       | 2      | 8
12       | 9         | 1      | 1       | 2      | 9
13       | 11        | 1      | 4       | 5      | 13
14       | 11        | 1      | 4       | 5      | 14

wp_sMake

makeId | MakeName
-------+---------
1      | Kia

wp_sModel

modelId | makeId | ModelName
--------+--------+----------
1       | 1      | Optima
4       | 1      | Sportage

wp_sYear

yearId | makeId | modelId | Year
-------+--------+---------+-----
1      | 1      | 1       | 2011
2      | 1      | 1       | 2012
3      | 1      | 1       | 2013
4      | 1      | 1       | 2014
5      | 1      | 4       | 2011
6      | 1      | 4       | 2012
7      | 1      | 4       | 2013

wp_sEngine

engineId | makeId | modelId | yearId | EngineName
---------+--------+---------+--------+-----------
1        | 1      | 1       | 1      | LX
2        | 1      | 1       | 1      | EX
3        | 1      | 1       | 1      | SX
4        | 1      | 1       | 1      | Hybrid
5        | 1      | 1       | 2      | LX
6        | 1      | 1       | 2      | EX
8        | 1      | 1       | 2      | SX
9        | 1      | 1       | 2      | Hybrid
10       | 1      | 1       | 3      | LX
11       | 1      | 1       | 3      | EX
12       | 1      | 1       | 3      | Hybrid
13       | 1      | 4       | 5      | Base
14       | 1      | 4       | 5      | EX
15       | 1      | 1       | 1      | LX
16       | 1      | 4       | 5      | SX
17       | 1      | 1       | 3      | SX

wp_postmeta

meta_id | post_id | meta_key | meta_value
--------+---------+----------+------------
20      | 9       | _sku     | 2T013-ADU00
24      | 9       | _price   | 65.60
50      | 11      | _sku     | 988503W000
24      | 11      | _price   | 15.75

Answer 1

One way of getting the price and the sku from the wp_postmeta table is to join to wp_postmeta table twice.

So you would do something like

...
JOIN wp_postmeta sku ON filter.productId  = sku.post_id 
JOIN wp_postmeta price ON filter.productId  = price.post_id
...

And replace meta.* in your SELECT with sku.meta_value as sku, price.meta_value as price

Adjust other parts or the code/sql accordingly, but hopefully you get the idea.

Basically the idea is you need to join the table as the sku and as the price. Imagine you had a sku and price table, how would you do the join, same idea as far as the join is concerned, they are just in the same table.