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Asked: 2026-05-21T15:08:36+00:00

I have a table link_tabl in which I want to link three other tables

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I have a table “link_tabl” in which I want to link three other tables by id. So in every row I have a triplets (id_1, id_2, id_3). I could create for every element of the triplet a column and everything would be fine.

But I want more: =)

I need to respect one more “dimension”. There is an Algorthm who creates the triplets (the linkings between the tables). The algorithm sometimes outputs different linkings.

Example:

table_person represents a person.
table_task represents a task.
table_loc reüpresents a location.

So a triplet of ids (p, t, l) means: A certain person did something at some location.

The tuple (person, task) are not changed by the algorithm. They are given. The algorithm outputs for a tuple (p,t) a location l. But sometimes the algorithm determines different locations for such a tuple. I want to store in a table the last 10 triplets for every tuple (author, task).

What would be the best approach for that?

I thought of something like:
IF there is a tuple (p,t) ALREADY stored in link_table ADD the id of location into the next free slot (column) of the row.
If there are already 10 values (all columns are full) delete the first one, move every value from column i to column i-1 and store the new value in the last column.
ELSE add a new row.

But I don’t know if this is a good approach and if it is, how to realise that…

Own partial solution
I figured out, that I could make two columns. Onw which stores the author id. One which stores the task id. And by

...
UNIQUE INDEX (auth_id, task_id)
...

I could index them. So now I just have to figure out how to move values from column i to i-1 elegantly. =)

Kind regards
Aufwind

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1 Answer

  1. Editorial Team

    I would store the output of the algorithm in rows, with a date indicator. The requirement to only consider the last 10 records sounds fairly arbitrary – and I wouldn’t enshrine it in my column layout. It also makes some standard relational tools redundant – for instance, the query “how many locations exist for person x and location y” couldn’t be answered by “count”, but instead by looking at which column is null.

    So, I’d recommend something like:

    personID      taskID       locationID        dateCreated
1             1            1                 1 April 20:20:10
1             1            2                 1 April 20:20:11
1             1            3                 1 April 20:20:12

    The “only 10” requirement could be enforced by using “top 10” in select queries; you could even embed that in a view if necessary.

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