Hi I'm drawing an ER Diagram using MySQL Workbench for my final year project. It's about a shipping company, where buyer & shipping agent are involved in a shipping process with my client.
So far the buyer and agent have same attributes. So I decided to keep both of their data in a table and differentiate them using an attribute (type in my case).
As you see in my picture I couldn't able to make a N:M relationship between shipping table and external table. It always give me 1:M relationship. When I try to do the relationships manually it creates a another relational table and make a 1:M relation with it.
Can anyone assist me with my problem? Further how efficient to have a relational table in my case.
Related
I need to create such a structure, there is a category of products, each category stores its own information, for example, be entered phone information when selecting a phone category, computer information must be entered when selecting a computer category, How to create this structure in a clean database? , how is it done in a real project?
Before creating a 'structure' in a DB you need to design your Entity-Relationship Diagram.
This means that you need to decide the Entities of your problem, these would be your tables later in the DB, the Relationships between the entities, these have multiple ways that can be depicted in the tables based mainly on their cardinality and then the properties of the entities, which will be the fields of the tables in your DB.
I think that you need to start from that, create the ER Diagram and then try to model it into the DB.
I have a simple and probably. banal question. I am working on the first, conceptual phase of an entity-relationship diagram.
This DABMS will be used by some Managers, that will control (registrate and modify accounts) of customers.
In my diagram I have the two entities "MANAGER" and "CUSTOMER". Is it necessary to connect them with a relationship (M:N), to specify that the Managers are those who will manage the customers' account, or this relationship is unnecessary?
to specify that the Managers are those who will manage the customers
No. ER diagrams typically show relations that are reflected in your database.
Example, what would be visible in your ERD
Each customer has a manager assigned who's responsible for this customer => 1:n - each customer has one manager but one manager can be responsible for multible customers.
I made an EER diagram in MySQL. The end goal is to be able to have a few tables (fleet1, fleet2, fleet3) that are comprised of a unique certificate id, but have multiple vendors and multiple vessels. In each fleet, the vendor can appear more than once, but each vessel only once. When everything is complete, I will connect this database to mail merge and be able to query data from each fleet.
I want to see all of the columns from the vendor table, as well as all of the columns from the vessel table inside of each fleet table
Would a linking table suffice to link the tables?
I tried a one-to-many (creating a linking table which would be each fleet table), but I want each fleet table to comprise of all of the vendor information and all of the fleet information, so that when I do a mail merge I see certificate id, all vendor info, and all vessel info.
I am in 2NF, but can I simplify further into 3NF?
I used the Forward Engineer tool in the MySQL Workbench to generate a database based on the tables I entered. I was able to populate my tables, such as "Villagers," "Fish," and "Items" for the database I am building around the game Stardew Valley. However, when I linked the tables in the ER Diagram it created new tables based on relationships, such as Cooking_Has_Fish because many fish can be used in many recipes and many recipes can use many fish. But, once I populated the Cooking and Fish tables there was nothing in the generated Cooking_Has_Fish table. I am trying to understand how this table functions or how it can be used, or if it needs to be populated and I missed something.
Thanks for reading.
No table ever gets populated on its own, you need to make sure that it gets populated. The third tables created for many-to-many relationships are called associative or junction table and as a minimum contain the primary keys of the 2 tables they join.
If you have a recipe_id identifying recipies and a fish_id identifying fishes, then Cooking_Has_Fish table would have at least a recipe_id and a fish_id field.
If you want to associate fish and chips (with recipe_id 1) with cod (fish_id being 2), then you would do the following insert:
insert into Cooking_Has_Fish (`recipe_id`, `fish_id`) values (1,2)
This means the cod is required for the "fish and chips". You may add additional fields to your association table, such as how much cod you need for the fish and chips.
In summary: you have to populate your association tables based on how you would like to associate your entities (tables) that have many-to-many realationship with each other.
For example if I have 20 tables, I have to design it by section? i.e
CLIENT (id, name...) -- orders -- ODERS_DETAIL(id, products...)
.
.
.
lives --- ADDRESS(...)
Or I can use The MySQL Workbench EER Model (To me, it looks like the Pysical Model)?
Or like this: Data Modeling Levels
Well, I would not do it in code. That is for the RDBMS itself.
MySQL EER Workbench does not do true entity modeling - it is modeling tables, you are correct.
If you want true ER modeling I suggest Oracle's newly released ('Early Adopter') SQL Developer Data Modeler.
It is pretty easy to use, is free and can forward and reverse engineer models to tables. http://www.oracle.com/technetwork/developer-tools/datamodeler/overview/index.html
When in doubt, design a table that is totally flat, and then determine where you have duplicated data, these can be considered for tables (entities).
The "ER model" defines entities unto themselves and allow the reference of entity-to-entity (table-to-table) through a separate relation. If you can remove yourself from thinking about foreign keys in your entities and focus on the relations in their own separate table.