Question

My MySQL query keeps creating duplicate entries. I think it is to do with my join or ID values.
I am new to JOIN and I am trying to do a fairly simple JOIN and filter.

Basically I am filtering products on a product listing page.

newCatCols

+----+-----------------+-------------+
| id | sku             | name        |
+----+-----------------+-------------+  
|  1 | 670_apple       | Black       |
|  2 | 670_apple       | Apple       |
|  3 | 670_apple       | Blush       |
|  4 | 670_apple       | Turquoise   |
|  5 | 670_apple       | Light Coral |
| 10 | 640_apple_black | Apple_Black |
| 22 | 347_blush       | Lime        |
| 33 | 347_blush       | Turquoise   |
| 44 | 347_blush       | Gray        |
| 55 | 347_blush       | Yellow      |
+----+-----------------+-------------+

newCatProds

+----+-----------------+--------+------+
| id | sku             | cost   | cat  |
+----+-----------------+--------+------+    
|  1 | 670_apple       | 489.55 | swar |
| 10 | 640_apple_black | 458.99 | swar |
| 22 | 347_blush       | 741.44 | sig  |
+----+-----------------+--------+------+    

If the custom chooses Black, I want it to return colours with Black, and Apple_Black and Apple. It just duplicates listings though:

// productslisting.php?cat=swar&filter=Black
$strColourGet=mysql_real_escape_string($_GET["filter"]);
$strCatGet=mysql_real_escape_string($_GET["cat"]);  

if($strColourGet=="Black"){

$checkSQL=mysql_query("
SELECT * FROM `newCatProds`
INNER JOIN `newCatCols`
ON `newCatProds`.`sku` = `newCatCols`.`sku`
WHERE (
    `name` = 'Black' OR
    `name` = 'Apple' OR
    `name` = 'Apple_Black' 
)
AND `status`='1' AND `category` = '".$strCatGet."'
ORDER BY `newCatProds`.`rank` DESC");

}

Results appear twice though. Can I somehow not have it appear twice?

710     702_appleblack  139         sig     0   8   1   1   1243    702_appleblack  Apple_Black
486     613_turq    139         sig     0   124     1   1   695     613_turq    Black
463     379_sapphire2   139         sig     0   46  1   1   652     379_sapphire2   Black
504     670_apple   119         sig     0   176     1   1   607     670_apple   Black
463     379_sapphire2   139         sig     0   46  1   1   658     379_sapphire2   Apple_Black

So maybe a group? So the 379_sapphire2 should only appear ONCE as it has both in?

Answer 1

Those are all distinct results. Look at them more closely.

If you want to avoid this, instead of SELECT * FROM do a specific field(s) request.

To get only one answer, you need to specify that field in select as distinct and create a group_by clause. You can’t create a group by with * in select parameters.

PS: I would suggest you rewrite your query something like this. It is easier to understand that way:

SELECT
    DISTINCT( category )
FROM
    newCatProds p
JOIN
    newCatCols c
ON
    p.sku = c.sku
WHERE
    c.name IN ( 'Black', 'Apple', 'Apple_Black' )
    AND status =  1
    AND category = '" . $strCatGet . "'
GROUP BY
    category
ORDER BY
    p.rank DESC;