在MySQL中使用内部联接是否可能？

Question

I'm stuck on trying to build a query that will include a given order_reference cover file from the data sample below only if ALL of the print_item_qty values of the files under the same order_reference are equal to 5.

Is this possible using joins or is this outside the remit of a single query?

I've tried building inner joins but cannot work out how to restrict the results so that I only get a cover row when all the component parts of an order have equal values in the print_item_qty column.

Here is the base SELECT query and sample data:

SELECT c1.`order_id`,c1.name1,c1.name2,c1.`print_item_qty`,c1.`sub_item_type`,
c1.`order_reference` FROM print_items;


+--------------+-------+---------+----------------+---------------+-----------------+
| order_id     | name1 | name2   | print_item_qty | sub_item_type | order_reference |
+--------------+-------+---------+----------------+---------------+-----------------+
| 000003201875 | Jason | Bramley | 5              | cover         | 1875            |
| 000003201875 | Jason | Bramley | 5              | inner         | 1875            |
| 000003201875 | Jason | Bramley | 1              | card          | 1875            |
| 000003201876 | Jason | Bramley | 5              | cover         | 1876            |
| 000003201876 | Jason | Bramley | 5              | inner         | 1876            |
+--------------+-------+---------+----------------+---------------+-----------------+

My desired result for the above sample data would be only the following row:

+--------------+-------+---------+----------------+---------------+-----------------+
| order_id     | name1 | name2   | print_item_qty | sub_item_type | order_reference |
+--------------+-------+---------+----------------+---------------+-----------------+
| 000003201876 | Jason | Bramley | 5              | cover         | 1876            |
 +--------------+-------+---------+----------------+---------------+-----------------+

Any help anyone could give to point me in the right direction would be greatly appreciated.

Many thanks.

Answer 1

So you want to verify that you only select data for orders for which the print_item_qty = 5 for all sub_item_type in that order_reference.

To do this, use a subsquery like

SELECT order_reference, 
MAX(print_item_qty), 
MIN(print_item_qty) 
FROM print_items
GROUP BY order_reference 
HAVING MAX(print_item_qty) = 5
AND MIN(print_item_qty) = 5

And join to your original dataset. The subquery will restrict to the ids you want, and joining back will return all rows associated with the order_references for which print_item_qty = 5 for every sub_item_type, eg,

SELECT c1.`order_id`,
c1.name1,
c1.name2,
c1.`print_item_qty`,
c1.`sub_item_type`,
c1.`order_reference` 
FROM print_items AS c1
INNER JOIN (SELECT order_reference, MAX(print_item_qty), MIN(print_item_qty) FROM print_items
GROUP BY order_reference HAVING MAX(print_item_qty) = 5 AND MIN(print_item_qty) = 5) AS b
ON c1.order_reference = b.order_reference