引用2个不同表的列

Question

Following schema:

archivebox (id, mediatype_id)
mediatype (id, name)
archivebox_records (id, archiveboxId, recordId)
picture (id,name)
print (id,name)

recordId should be referenced whether to pictureId or printId. How is it possible to solve this problem? I work with mysql.

Thanks!

Answer 1

It's always best to be explicit in your designs. This would involve creating two tables archive_pictures and archive_prints with foreign key relationships to the respective tables.

If you really don't want to go down that route, try adding some sort of record indicator to the archive_records table, eg

ALTER TABLE `archive_records` ADD `record_type` ENUM('picture', 'print') NOT NULL;

You can then create queries based on this indicator

SELECT p.name FROM picture p
INNER JOIN archive_records ar
    ON ar.record_type = 'picture' AND p.id = ar.recordId

Answer 2

Another clean solution is to merge picture and print into

medium( id, name, type)

where type can be "print" or "picture" or when the datamodel grows the foreign key referencing a table containing the allowed values.