Hi I am creating a ER diagram for my organization. How can i get the relationship between the tables in snowflake
Thanks
If you are trying to reverse engineer a current Snowflake database, you may have trouble. Foreign key constraints can be included in the table definition, however they are not enforced. If your developers included the constraints when they defined the tables, you can get the relationship from the table definitions. It is a good practice to include the constraints as many third party tools use them.
Do a deep study of all the relations of tables.
And try writing all the conditions on which two or more tables are connected
SELECT
`TABLE_NAME',
`COLUMN_NAME`,
FROM `YOUR_DATABASE`
WHERE 'PUT YOUR CONDITIONS '
This should solve your question
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I need to create a bus matrix and in order to do that i need to know which fact table has relationships with which dimension tables.
Unfortunately, in this new project I'm in, it seems to be no FK (crazy, i know).
What I thought about is to use ETL queries and check the joins between the Fact table with the dimension tables.
What I'm worried about is that there might be more relationships that are not included in ETL queries...any advice?
You can use the system metadata tables to list the foreign key references:
select tbname, pkcolnames, reftbname, fkcolnames, colcount
from SYSIBM.SYSRELS B;
If the database does not have properly declared foreign key relationships, then the database does not have the information you are looking for.
Assuming the DB holds no information about the FKs (or information that would help you derive them, like identical column names) then, as you mentioned, examining the ETL code used to load each fact table is probably the only other way of doing this. The ETL must be running a look up on each dimension to get the PK to insert into the fact record, so the information will be there.
There shouldn't be any relationships involving facts that you couldn't determine with this approach. There may be additional relationships between dimensions (bridge tables, more complex SCD types, etc.) but if you sorted out the fact relationships then what remains should be a small enough subset to resolve manually (i.e. by intelligent guesswork)
Good Morning,
in the design of a database, I have a table (TabA's call it) that could have relationships with four other tables. In the sense that this table can be connected both with the first of four, and with the second, and the third to the fourth, but could not have links with them; or it could have one (with any of the tables), or two links (always with two of any of them), and so on.
The table TabA I added four fields that refer to the four tables which could be "null" when they do not have any connection.
Wondering is this the kind of optimal design (say the four fields in the TabA) or you can make a better design for this type of situation?
Many thanks for your reply.
dave
In answer to the question and clarification in your comment, the answer is that your design can't be improved in terms of the number of foreign key columns. Having a specific foreign key column for every potential foreign key relationship is a best practice design.
However, the schema design itself seems questionable. I don't have enough information to tell whether the "Distributori_[N]_Livello" tables are a truly hierarchical structure or not. If it is, it is often possible to use a self-referential table for hierarchical structures rather than a set of N tables, as the diagram you linked seems to use. If you are able to refactor your design in such a way, it might be possible to reduce the number of foreign key columns required.
Whether this is possible or not is not for me to say given the data provided.
in a relational database, can we have a table without any relation with the other tables?
Yes. The way relations are expressed are with foreign keys. If a table you generate has no Foreign keys, and no foreign keys in other tables point to this table, it has no relationships.
It can still be given a relationship later though so don't worry about shooting yourself in the foot.
Of course. Even you can create a table without fields.
Yes you can. Tables do not have to have any relation to each other. Relations can always be added through the use of foreign keys if you want to add them later.
I'm creating a company management database and I have a "Company_Expenses" table that I just need for summery reports on the Company's revenues. I can't think of anything this table might need to be connected to so it's just on it's own for now.
Your question belies a larger problem with your understanding of databases.
A relation is a set of tuples (a relation can be thought of as a table).
A tuple can be thought of as a row.
Relationship in English means connectedness and has nothing to do with relation from relational databases.
Both relation and relationship share word roots, but in database theory, these words/concepts do not have anything to do with each other.
The root of the word relation in database theory comes from math (see function vs relation).
I have a trip (primary: idTrip), where I can link more packages (primary: idPackage), so, I got a relationship table to link trips with packages (primary: idRelTripPackage). (relationship n-to-n)
And next I got a registrations table (primary: idRegistration). How do I best link those (1-to-1 relationship)?
I add two columns in the registrations table (idTrip, idPackage)?
I add a relationship table where i link idRegistration, idTrip, idPackage?
I add a relationship table where i link idRegistration, idRelTripPackage?
Am I right in thinking the relation from Registrations is to RelTripPackage, and its definitely one-to-one. There are a couple of options:
1: As it really is a one-to-one there's not really anything to stop you putting the Registrations data directly onto RelTripPackage, or doing the vice-versa and putting idPackage and idTrip straight onto Registrations as FKs, with a unique key across the two FK columns to ensure there aren't duplicates.
2: If do want the two separate tables then just add idRetTripPackage to Registrations as an FK, and then add a unique constraint on it - again to ensure uniqueness.
There's no need for a separate relationship table as its a 1-1 relationship - They only really become relevant when you are using an n-n. The rest of the time FKs should be placed directly on the child table.
If you follow that logic, you will
add tables and Relations every time you need to add Relations
end up with confusing or duplicate Relations (multiple paths between any two tables)
However the problem (limiting factor) is that the tables you are starting with are not actually normalised. Since the starting position does not have a good basis, you will end up with far more Relations (in tables) than there actually are between the Entities. So the best advice is, the Best practice is, before you attempt this current extension, step back and normalise the data, the existing tables. Then the extension will be much easier, and you will end up with less tables.
if you provide info re the tables (Person, Trip, Package, etc); what exactly is a Registration, etc ... I can provide more explicit answers.
Generally any attribute that is 1::1 with the PK of an Entity should be an attribute in that entity. Any attribute that is 1::0-1 with the PK of an Entity should be in a separate table.
ER Diagram
Based on the information provided, this is your ▶Entity Relation Diagram◀. As long as you use Relational Identifiers, all the Relations you have identified thus far are supported directly (otherwise, if you use IDs, you will need more Relations and tables).
Readers who are unfamiliar with the Relational Database Modelling standard may find ▶IDEF1X Notation◀ useful.
If I was asked to query JOIN of more than three tables, what is the best way I go about understanding the relationship of the tables before I code. Should I use Database Diagram in SQL Server, or would I be given the necessary information? What would you recommend?
Thanks in advance for your time.
You could use the diagramming tools in SQL Server Management Studio to discover any Foreign Key relationships between those tables. It might be quicker than using the GUI to inspect each table in Design mode, and viewing its Relationships dialog.
Consider creating an ad-hoc View with those 3 tables. This will help you produce the SQL statement that you'd need. If any relationships exist on those 3 tables, you'll have the JOIN statement created for you by the tool.
Right click Views -> New View.
Pick the tables you need, click Add
all relationships are displayed in the Diagram Pane, and the SQL Pane will the SELECT statement with the required JOINS.
Depending on the convention they use for creating foreign keys, it shouldn't be to hard to find the relationships between tables.
The convention we use is
dbo.TableA(ID PK)
dbo.TableB(ID PK, TableAID FK)
dbo.TableC(ID PK, TableBID FK)
...
If they don't use any convention at all or didn't even create Foreign Key constraints, you can take that as an opportunity to educate them about the importance of conventions aka the lost time and money by not using them.