Is it possible to have a MySQL column containing multiple values as foreign keys?

Question

I am learning MySQL and have MariaDB installed in Fedora 19.

I have a scenario where I require a column to contain multiple values in order to reduce possible redundancy of column allocation.

In the example below, is it possible to have each value in the tags column of the log table reference the tag_id column in the tags table?

users

user_id        |
1              |

activities

activitity_id  |
1

log

user_id        |    activity_id    | tags
1              |    1              | 1,3,5 # multiple foreign keys?  

tags

tag_id         |
1              |
2              |
3              |
4              |
5              |

If it is not possible, could anyone provide the logic for the most feasible solution based on the data scenario above?

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Answer 1

If you do not wish to make up a "middle man" table for linking the two tables you can have a comma separated value in the field, you would just need to use the find_in_set mysql function when doing queries

USING find_in_set

SELECT
   log.user_id, log.activity_id, log.tags,
   GROUP_CONCAT(tags.name) as taggedNames //This assumes there is a field called `name` in tags table
FROM
   log
LEFT JOIN tags
ON
   FIND_IN_SET(tags.tag_id,log.tags)
GROUP BY
   log.activity_id

GROUP_CONCAT will group together a field and separate them by a deliminator, default is ,