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When relations between tables are created it becomes very difficult to edit tables, drop and re-create them. well I decide to leave creating relations for when the job is done and that time its not easy either and later some tables might need modifying again.
what is the best practice for creating foreign keys, and all other relations?
In big projects that I devide project to several small projects, well sometime in one of the smaller projects I see that I have to make a small change to previous small projects. and this ruins everything.
I always create relations when I create my initial database structure, and because it is normally (sometimes... once was...) designed properly, the relations don't tend to change.
What you may find eases any changes to the tables is to change one of the options
In Tools-Options, choose Designers - Table and Database Designers and clear the checkbox marked Prevent saving changes that require table re-creation
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I created 2 database designs (External & Internal Database). But I'm not sure if that fits in terms of relationship, normalization, logic, redundancy, ....
I also created 2 versions of the database design (The first one without mapping table and the second with). It's in German, I hope that's okay for you.
Do these designs meet typical relational database criteria such as 3NF, and do they specify the entity relationships in a clear and maintainable fashion?
database design 1
database design 2
Edit:
current database design
The ER diagram is OK of both internal and external because it is normalized, no redundancy, no many to many relationships and there is no functional dependency between fields except on the key.
I have a couple of comments about the diagram linked as "current database design":
The BM_Mapping table should use M-ID as its foreign key rather than Meeting_ID. The current design prevents any change to a value in the column Meeting.Meeting_ID.
I would keep the same primary-key naming convention in the Visitor table as used in the other tables. So V-ID rather than Visitor_ID
Apart from these comments, the rest of the design meets the standard RDBMS 3NF and entity relationship standards.
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Often we come across some small insignificant (debatable) tables left out as stand alone. Although they are used in joins (sparingly) but still developers don't bother to relate them.
May be too many References made the inserts slow.
This leads to this question :
As a thumb rule should we relate all the tables in the database ? If no then where to draw the line?
thanks
Foreign Keys are not always a negative impact to performance, they can be a positive impact as well. Database relationships do more than just ensure referential integrity, they also help teach SQL Server about the nature of your data. The fact that two fields are related can give clues as to the cardinality of your queries and thus the optimizer actually takes these relationships into consideration when it's estimating the cost of your query.
In my opinion, if two fields are related in your database, they should have a defined relationship. In general, the more you can teach SQL Server about your data (not just relationships, but CHECK constraints as well), the better it will be at generating efficient query plans. Of course like anything in SQL Server, there are exceptions to the rule, but if you want a rule of thumb, I would lean toward defining all the relationships.
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How I can come up with an effective BodyBuilding database, what entities are most important?
From which I should be able to come up with an ER diagram. I'm still a novice to databases, but I have read quite enough, most difficult I'm finding a problem with differentiating between a Gym database and BodyBuilding Club database.
Have you tried listing everything you think relates to the database, then removing the ones you don't like, then grouping them in a way that makes sense to you or users of the database?
Certification types, access to bodybuilding books, bodybuilding trainers, ease of super sets, free weight ratios, ratings from heavy lifters, etc.
Try everything, make a list, narrow it down to the items needed for proper function and your business perspective (safety, legal, etc).
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There is so much conflicting and confusing advice all over the web about this. And I would like to settle this for myself and for any one who will be looking for such information in future.
Question is — Will Entity frame work work well with database that has tables with no Primary keys.
Detail : I have a database and it has lots of tables that don't have a PK specified. Call it bad design or whatever, but there is nothing I could do to change the schema now. I have to work with it. And we would like to use EF because we like MS and we work with MS tools all the time. We sleep much easier knowing MS will keep updating and supporting this EF, with its full attention in future. Okay here now is my burning question which I have researched excessively on this website and others. "Can I use EF in my project fully knowing that my DB has some tables that will never have PKs" . Part of the problem is we really want to use EF for ease of use and we being MSphiles.
I have heard lot of advice ranging from:
It wont work.
It can be made to work.
Not a big deal at all...
That's where it gets really sick. Please advise.
Well, it largely depends on how you intend to use it. Without a primary key, you can't have referential integrity. So, in effect you can't have automatic lookups of subtables and such.
You can do manual joins of tables, and that should work.. but that severely limits the functionality of EF.
But here's the thing, nothing we say can convince you. What will convince you is doing it yourself. Build a test database, and a test app. Setup your EF database. See if it works for you.
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I have a database design issue and I'm not sure which of my alternatives I should go with.
I have a system that shows a politician's votes on every issue. Users can log in and "support" that politician on each issue. I'm not sure how the associations should work. Here is a picture of two alternatives:
http://i1068.photobucket.com/albums/u447/dmoss18/ScreenShot2012-05-03at111656AM.png
Option 1: A politician has many votes on many issues. A user supports each politician's vote.
Option 2: A user supports a politician on a certain issue (an association table with three foreign keys).
Is option 2 not feasible at all? Is it bad practice to associate three tables in one entity? Which option is considered best practice?
I would prefer option (1) because it shows that the user supports the particular vote. In option (2) it would seem to be possible (without additional constraints) for a user to support a certain politician on a certain issue when that polititian has never voted on it at all! (Of course if that is a desirable possibility then you must go for option (2)).