内部联接2张桌子多个结果

Question

i have 2 tables, one for the products and one for the sizes. they have a relation with fk and the problem is that when I'm using the inner join I cannot use the "group by" in order to don't have repeated results. this is the code:

SELECT
sneakers.sneaker_id,
sneakers.sneaker_name,
sneakers.gender,
sneakers.description,
sneakers.price,
sizes.size,
brand_names.brand_name
FROM sneakers
INNER JOIN sizes ON sneaker_fk = sneaker_id

if i try to use the GROUP BY sneaker_fk it will give me this response:

Error
SQL query: Documentation


SELECT sneakers.sneaker_id,sneakers.sneaker_name, sneakers.gender, sneakers.description,
                                    sneakers.price, sizes.size, brand_names.brand_name FROM sneakers
                                    INNER JOIN sizes ON sneaker_fk = sneaker_id
                                    INNER JOIN brand_names ON brand_name_fk = brand_name_id
                                    GROUP BY sneaker_fk LIMIT 0, 30
MySQL said: Documentation

#1055 - Expression #6 of SELECT list is not in GROUP BY clause and contains nonaggregated column 'sneakerstore.sizes.size' which is not functionally dependent on columns in GROUP BY clause; this is incompatible with sql_mode=only_full_group_by

What am I doing wrong?? Do you have any better solution to display One item with all the related sizes without having multiple results?

I hope you can help me as fast as possible! thanks in advance

Answer 1

Use MySQL's Group_Concat() function

The MySQL GROUP_CONCAT() function returns a string with concatenated non-NULL value from a group.

Excerpt from Using GROUP_CONCAT with joined tables

GROUP_CONCAT works with joins as well.

Let's say we have a table courses:

  | id | name |
  +—-+—————+
  | 1 | Ruby 101 |
  +—-+—————+
  | 2 | TDD for Poets |
  +—-+—————+'

We also have a second table bookings:

  | id | course_id |
  +—-+———–+
  | 7 | 1 |
  +—-+———–+
  | 8 | 1 |
  +—-+———–+
  | 9 | 1 |
  +—-+———–+
  | 10 | 2 |
  +—-+———–+
  | 11 | 2 |
  +—-+———–+


SELECT courses.name, GROUP_CONCAT(bookings.id)
FROM bookings
INNER JOIN courses ON courses.id == bookings.course_id
GROUP BY bookings.course_id;

The result set looks like this:

| courses.name | GROUP_CONCAT(bookings.id) |
+—————+—————————+
| Ruby 101 | 7,8,9 |
+—————+—————————+
| TDD for Poets | 10,11 |
+—————+—————————+