Question

I am trying to write a SQL query that pulls from 3 tables and haven’t been able to achieve the results I need. I want to return all the property names (labels) that are paired with a particular category and pair those properties with the values from a particular asset from the said category, which may not have a value to pair with each property.

I want all the properties for category 4, paired with the values for asset 135. Asset 135 doesn’t have values set for property 3 or 4, so I want:

| property_name | property_value     |  
|:--------------|:-------------------|  
| Fixture ID    | A5                 |  
| Manufacturer  | Black & Decker     |  
| Model #       |                    |  
| Type          |                    |

Here is my query:

SELECT property.property_name, asset_property.property_value
FROM property
LEFT OUTER JOIN category_property
ON property.property_id = category_property.property_id
INNER JOIN asset_property
ON asset_property.property_id = property.property_id
WHERE category_property.category_id = 4
AND asset_property.asset_id = 135

resulting data:

| property_name | property_value     |  
|:--------------|:-------------------|  
| Fixture ID    | A5                 |  
| Manufacturer  | Black & Decker     |  

It’s missing 2 of the properties because of my AND asset_property.asset_id = 135

Here are the tables:
* asterisk just indicates rows from test case.

table: property

| property_id | property_name |  
|:-----------:|:--------------|  
| 1           | Fixture ID    |*  
| 2           | Manufacturer  |*  
| 3           | Model #       |*  
| 4           | Type          |*  
| 5           | Lamp Type     |  

table: asset_property
pairs assets with property values.

| asset_id | property_id | property_value |  
|:--------:|:-----------:|:---------------|
| 129      | 1           | A5             |  
| 129      | 2           | Black & Decker |  
| 129      | 3           | 1230-02        |  
| 129      | 4           | Incandescent   |  
| 135      | 1           | E6             |*  
| 135      | 2           | Linden         |*  
| 147      | 1           | G1             |  

table: category_property
pairs categories with its properties.

| category_id | property_id |  
|:-----------:|:-----------:|  
| 4           | 1           |*  
| 4           | 2           |*  
| 4           | 3           |*  
| 4           | 4           |*  
| 7           | 2           |  
| 7           | 5           |  

I’ve tried all the different JOIN types, HAVING, GROUP BY….can’t it figure out. If anyone understand what I need, I’d really appreciate the help! Thanks!

---

To clarify, I need to return these sets of results:

| property_name |  
|:--------------|  
| Fixture ID    |  
| Manufacturer  |  
| Model #       |  
| Type          |  

AND

| property_value |  
|:---------------|  
| A5             |  
| Black & Decker |  

And join them on property_id:

| property_name | property_value |  
|:--------------|:---------------|  
| Fixture ID    | A5             |  
| Manufacturer  | Black & Decker |  
| Model #       |  
| Type          |  

But since there is no record for property_id 4 and 5 in the asset_property table, the property_name for those properties aren’t shown.

| property_name | property_value |  
|:--------------|:---------------|  
| Fixture ID    | A5             |  
| Manufacturer  | Black & Decker |  

Model #
Type

I want them to e shown. I want ALL the property names for Category 4 to be returned and be paired with any matching property_values for Asset 135.

---

So for the Fruits Category I want all the properties names returned (Color, Season, Taste). The color property for Apple is not set, but I still want all the property types to be returned, so they can be changed or filled out:

| property_name | property_value |  
|:--------------|:---------------|  
| Color         |                |  
| Season        | Fall           |  
| Taste         | Tart           |  

Answer 1

Just change the INNER JOIN to a LEFT OUTER JOIN, and move AND asset_property.asset_id = 135 from the WHERE clause to the ON clause:

SELECT property.property_name,
       asset_property.property_value
  FROM property
 INNER
  JOIN category_property
    ON property.property_id = category_property.property_id
  LEFT
 OUTER
  JOIN asset_property
    ON asset_property.property_id = property.property_id
   AND asset_property.asset_id = 135
 WHERE category_property.category_id = 4
;

(I’ve also changed the first LEFT OUTER JOIN to an INNER JOIN, since the WHERE category_property.category_id = 4 will (correctly) filter out records where the join fails, anyway.)