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How-to store multiple values in one DB column?

Posted on 2007-10-14
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Hi! Currently I'm developing simple db catalog application for dvd store in C# using DataSets. I have stumbled upon the following problem. imagine i have two tables in dataset:
MOVIES with columns - id, name, actorId
ACTORS with columns - id, name
Currently i have set ACTORS.id as a parent in relationship with MOVIES.actorId (child). however this way i am able only to specify one actor per movie which is bad since movie usually have more than one actor acting. also note that number of actors per movie is dynamic - it can be 2, 5 or 20 and it would be dumb to create 20 or 50 actor columns in MOVIES table.. so how do i solve this problem?
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Question by:latsubs
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Guy Hengel [angelIII / a3] earned 200 total points
ID: 20073181
that is a database design issue.
you will need the design to be like this:

MOVIES with columns - id, name
ACTORS with columns - id, name
ACTOR_IN_MOVIE with columns actor_id, movie_id

and voila, you can define which actor is in which movie.
this is called a MANY - to - MANY relationship, and should be implemented like this for best performance and best scalability.
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by:latsubs
ID: 20073411
thank you. that explains much.
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by:latsubs
ID: 20076189
however i have one more question regarding table ACTOR_IN_MOVIE - how should i set indexing? should i set as index both fields? or create field id?
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by:Guy Hengel [angelIII / a3]
ID: 20076203
you would usually create 2 indexes. one with both fields, and one with the field you specified second it the other index.
so either 1 index with ACTOR_ID+MOVIE_ID  and the second index with MOVE_ID alone
or 1 index with MOVIE_ID + ACTOR_ID and the second index with ACTOR_ID alone.
the index with the 2 fields should then be defined as primary key, unless:
>or create field id?
you do that: create a dedicated primary key field.
note: you might want to add other fields to this table, for example, a property that specifies if the actor was a main actor, a second role or even on a statist / double etc...  or another property saying if the actor, for that performance, got an oscar or something else ....

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