SQL - Get rows with one result and selected option - Relation Table - mysql

Question

I have a table that has the relations of products and colors. Each product has one or multiple colors. Is it possible to do a query that returns only the products that have one color only and the color wanted ?
Value from the api : color_slug = white ;
Sample table :
color_table
+----------+------------+
| color_id | color_slug |
+----------+------------+
| 1 | white |
| 2 | blue |
| 3 | black |
| 4 | green |
| 5 | red |
| 6 | yellow |
+----------+------------+
product_table
+------------+--------------+
| product_id | product_name |
+------------+--------------+
| 1 | shoes |
| 2 | shorts |
| 3 | t-shirt |
| 4 | jacket |
| 5 | watch |
| 6 | glasses |
+------------+--------------+
pc_relation
+----+------------+----------+
| id | product_id | color_id |
+----+------------+----------+
| 1 | 1 | 5 |
| 2 | 1 | 1 |
| 3 | 2 | 1 |
| 4 | 2 | 4 |
| 5 | 2 | 3 |
| 6 | 3 | 2 |
| 7 | 4 | 1 |
| 8 | 5 | 5 |
| 9 | 5 | 6 |
| 10 | 6 | 1 |
+----+------------+----------+
Select unique color values (if i put WHERE color_id = 1 the product colors are not longer of one color only) :
SELECT product_id
FROM pc_relation
// WHERE color_id = 1
GROUP BY product_id
HAVING MIN(color_id) = MAX(color_id)
pc_relation.id = 6,7,10
SELECT *
FROM color_table
INNER JOIN pc_relation ON pc_relation.color_id = color_table.color_id
INNER JOIN product_table ON pc_relation.product_id = product_table.product_id
WHERE colors.color_slug = 'white'
Values wanted (color_slug = white):
pc_relation.id = 7,10
product_table.product_name = jacket, glasses
*all the combinations are unique and indexed. For example I cannot have one product with the same color
twice.

Answer 1

You are on the right track with your first query. Move the color comparison to the HAVING clause:
SELECT product_id
FROM pc_relation
GROUP BY product_id
HAVING MIN(color_id) = MAX(color_id) AND
MIN(color_id) = 1;
You can also phrase this using NOT EXISTS:
select r.*
from pc_relation r
where r.color_id = 1 and
not exists (select 1
from pc_relation r2
where r2.product_id = r.product_id and r2.color_id <> r.color_id
);
However, the GROUP BY method is more general.