I work with the MySQL database and I have 2 tables namely vortex and the edge. I provided it below,
Is this one-to-many relationship exists between the tables ? Some explanation will be helpful.
There are two one-to-many relationships because each vertex can be the source or the destination of many edges, but each edge can only have one source and one destination.
Speaking in terms of rows in the tables, you will have each vertex id appearing only once in the vertex table, but potentially more than once in the vertex_src_id and in the vertex_dst_id columns of the edges table.
You have two relation between these tables both one-to-many (one to (one or many ) )
one is based
vertex_src_id
and the second on
vertex_dst_id
Related
I have two different models in two different PostgreSQL tables for which there's a relationship with objects in a third table. Objects in the third table can only be linked to one object in one of the other tables (think of the two tables as pictures and posts and the other table as comments).
I only need to read from these tables, I never have to add objects in them. I have also nearly no control over the way the tables are defined.
How would I setup this relationship in SQLALchemy so that I can query posts or pictures with their associated comments ?
I have 2 tables that needs to be joined wherein both of them can have as many of the other table.
A resident can have as many as relative and the relative can have as many as resident.
I need your opinion if this is a good way to join them properly. What I've done is I have a separate table that saves their respective ids.
I've attached a picture of reference. Thanks!
table picture
Yes, that is a classic relational implementation for a many-to-many relationship, implemented with an intersection table.
The following is an Entity Relationship of a a Baseball League.
I'm having a bit of confusion understanding Relations and Attributes of Relations.
An description of the diagram follows:
According to the description, Participates is a Relation and Performance is an Attribute (complex) of Participates.
Questions:
How do Participates Map to actual tables in a database?
Would there be a Participates table with the fields that define Performance?
{Hitting(AtBat#, Inning#, HitType, Runs, RunsBattedIn,
StolenBases)}, {Pitching(Inning#, Hits, Runs, EarnedRuns, StrikeOuts, Walks, Outs, Balks, WildPitches)}, {Defense(Inning{FieldingRecord(Position,
PutOuts, Assists, Errors)})}
Similarly are Plays_For, Away_Team and Home_Team also tables.
As you create tables in a database (say MySql) how are Relations differentiated from Entities / Objects like Player, Team and Game.
Thanks for your help.
Question 1: Participates would be an actual table with foreign key columns for Player and Game as well as the column(s) for Performance. All M-N relationships need to be modelled in a separate table.
Question 2: To keep it as a semi-decent relational DB you would have to separate all the info into separate columns so that each column would only hold one singular data. If you didn't separate the data you would break the first normal form and would probably run into problems later in the design.
Question 3: As these three are 1-N you could also implement them with columns on the N-side. In the Game table for example you could have two foreign keys to Team table as well as all the data about the relationships in columns. For claritys sake you could make those relationships as separate tables also. As a sidenote: are you sure Player-Team is a 1-N-relationship so that a if a player changes teams the history-info about the StartDate and EndDate of the previous team is immediately lost?
Question 4: They are all treated absolutely the same - no differentiation.
I want to know in what situations we create many to many relation. What is the need of doing such?
A quick search goes a long way. Though the following is for MS Access, the concept is the same for any relational database.
Via: office.microsoft.com - Create a many-to-many relationship:
You have a many-to-many relationship when a single record in one table
can relate to many records in another, and a single record in that
second table can also relate to many records in the first. For
example, say your company has several types of computers and several
technicians, with each technician certified to work on some, but not
all, of the computers. Each technician can be related to more than one
computer, and in turn, each computer can be related to more than one
technician.
To track who can work on a given machine, you create a many-to-many
relationship by adding the primary keys from both sides of the
relationship to a third table, called a junction or link table. In
other words, a many-to-many relationship is really just a pair of
one-to-many relationships.
Is it possible to do a many-to-many relation without a bridge table in SSAS ?
I have one fact table with SubjectId and another fact table with FK_SubjectId and many others keys (related to others dimensions).
In my view datasource the two fact table are connected to each other, but I can't chose the many-to-many relationship in the dimension tab ?
I'm I missing something maybe ?
Thanks a lot.
You would at least have to define an intermediate dimension. This can be defined based on the first of the fact tables, and can have the SubjectId as its only attribute. And this could be invisible to users. But Analysis Services requires an intermediate dimension for many-to-many relationships.
You can create a common table. this mean; For example you have two fact table create a table which includes only facts primary keys. Like this;
Select id as fact1ID , id as fact2ID from FactTable1 As F1
inner join FactTable2 As F2 ON F1.FK_ID = F2.ID
And create your measures in this hidden table. When you write your measure formula, dont use COUNT ,use DISTINCTCOUNT. Then create your relations from this common table to your fact tables. Now your fact table will works like dimension table. With this way you can take reports from all other dimension tables between eachother.