I would like to set an auto-update relationship between fields in two tables. One table contains information on the team and team leader, while the other table contains the team member name list with team and leader information included. I want the second table updated when the first table is updated (the team name is fixed and the team members always stay in the same team, while the team leader might be changed).
I set the team name as the primary key in the first table, and member name and team name as the primary key in the second table.
I want to use the relationship in Access, but it always shows: no unique index ... for primary table. Any instructions or help with any misunderstanding of the use of relationships is appreciated.
Since the Team Name is fixed, I would suggest creating a Team_ID field in both tables. Give each team an ID (it doesn't really matter what ID they get, so long as you're consistent across both tables) numbered 1 to however many teams you have.
Set the primary key in both tables to be Team_ID.
Set up a 1-to-Many relationship between the two tables, since you can have several team members on each team. Set that relationship up to be Cascading, and it will automatically update the second table when the first table is updated.
Also, I completely agree with ElectricLlama's statement above. Normalize your tables so you're only using each field a minimum number of times. Your first table should have Team_ID, Team_Name and Team_Leader, and your second table should have Team_ID and Team_Member. When you need to see the leader's info, join the two tables on Team_ID and bring in the necessary fields from each table.
Related
I am trying to simplify an application's database. In that database I have two tables let's say Patient and MedicalRecord. I know that two tables are said to be in One-to-One relationship iff that any given row from Table-A can have at most one row ine Table-B(It means there can be zero matchings).
But in my case, it is not at most, it is exactly. i.e., Every row in Patient should have exactly one row in MedicalRecord(no patient exist without a medical record).
Patient table has all personal details of the patient with his id as PK.
MedicalRecord talbe has details like his blood-group, haemoglobin, bp etc with his id as both PK and FK to the Patient.
My Question is, can I merge those two tables and create one table like,
PatientDetails : personal_details and blood-group, haemoglobin, bp etc
"bp" = "Blood pressure"? Then you must not combine the tables. Instead, it is 1:many -- each patient can have many sets of readings. It is very important to record and plot trends in the readings.
Put only truly constant values in the Patient -- name, birthdate (not age; compute that), sex, race (some races are more prone to certain diseases than others), not height/weight. Etc.
Sure, a patient may have a name change (marriage, legal action, etc), but that is an exception that does not affect the schema design, except to force you to use patient_id, not patient_name as a unique key.
Every patient must have a MedicalRecord? That is "business logic"; test it in the application; do not depend (in this case) on anything in the Database.
Both tables would have patient_id. Patients would have it as the PRIMARY KEY; MedicalRecord would haveINDEXed`. That's all it takes to have 1:many.
In situations where the tables are really 1:1 (optionally 1:0/1), I do recommend merging the table. (There are exceptions.)
If two tables have the same set of subrow values for a shared set of columns that is a superkey in both (SQL PRIMARY KEY or UNIQUE) then you can replace the two tables by their natural join. ("Natural join" is probably what you mean by "merge" but that is not a defined technical term.) Each original table will equal the projection of the join on that original's columns.
(1:1 means total on both sides, it does not mean 1:0-or-1, although most writing about cardinalities is sloppy & unclear.)
My UNF is
database(
manager_id,
manager_name,
{supplier_id,
supplier_name,
{order_id,
order_quantity}}
{purchase_id,
purchase_date}
Here manager_name, supplier_id, order_id and purchase_id are primary key.
During normalization there will be 1 table called purchase. Is it necessary to make manager_name as a foreign key?
How can I normalize these database?
This is a part of my college project on database. Normalization is really confusing.
First consider splitting things out by things that naturally go together. In this case you have manager information, supplier information, order information and purchase information. I personally would want to know the difference between an order and a purchase because that is not clear to me.
So you have at least four tables for those separate pieces of information (although depending on the other fields you might need, suppliers and managers could be in the same table with an additional field such as person_type to distinguish them, in this case you would want a lookup table to grab the valid person type values from). Then you need to see how these things relate to each other. Are they in a one to one relationship or a one-to many or a many to many relationship? In a one-to one relationship, you need the FK to also have a unique constraint of index to maintain the uniqueness. In a many to many you will need an additional junction table that contains both ids.
Otherwise in the simplest case the child table of purchase would have FKs to the manager, supplier. and order tables.
Manager name should under no circumstances be a primary key. Many people have the same name. Use Manager ID as the key because it is unique where name is not. In general I prefer to separate out the names into First, middle and last so that you can sort on last name easily. However in some cultures this doesn't work so well.
I'm running for office and have created a web app for tracking my door knocks to voters at their homes. The database contains a table called voters that contains all the necessary information about voters in my community.
I'd like to add a new feature to track donors to my campaign. Not all of these donors live in the community and do not vote in the district where I'm running for office. I do not need to track the same kind of info for these individuals as I do for the voters so I'm going to place these individuals into a table called nonvoters.
Now, the individuals in my "voters" table can also make donations, and I want to track those as well.
To track the donations from both voters and nonvoters, I'd like to set up a new table called "donations." This table would contain the appropriate details about the donation.
But I'm uncertain as to what the best structure is for linking the donations table to the "voters" and "nonvoters" table. If I create a column called voter_id in the table to key it to the donors information, there's no way to know which table that ID refers to. So do I set up two columns, nonvoter_id and voter_id and insert the ID into the applicable column depending on whether the donor is a voter? This seems weird.
Or maybe I create a column in both the voters and nonvoters table called donor_id that I can use to link my data in the donations table. If I went this route, it seems like I'd have to do a some behind the scenes work to ensure the donor_id was unique and was keyed to the data inside the donations table.
Or maybe there are other approaches I'm not familiar with. Any guidance is appreciated.
I would use a single table for voters and non-voters, let's say persons. You can have a flag in the persons table that indicates if the person is a voter or you may even derive this from their address (if that's possible).
I would create a donations table and link each donation to a person (or persons) in the persons table using the id in the persons table. If a donation can be given by multiple people, then you will need a 3rd connection table with person id and donation id as 2 fields. These 2 fields would be the primary key for the connection table.
I'm working on a very simple DB.
Imagine I've table customer and table seller.
The customer is able to request a quotation for some products
There will be a simple form that allow to customers to select products and submit the quotation.
Now, should I create table : "Quotation" and store all quotations (with id_quotation..etc)?
Thank you all
Without knowing all of the business rules that govern the requirements of this database, perhaps the following design will help to answer your question and explain a few concepts in the process.
In database terms, an entity is a person, place, or thing about which we want to collect and store data. From your description we can already see two entities: seller and customer. This is important since the entities we identify conceptually become database tables in their own right.
The seller table should contain data applicable only to sellers. Thus, the qualities (attributes) about sellers that we want to store become columns in our seller table. Each row (record) in the seller table represents an individual seller. Each individual seller is uniquely identified in the seller table with a unique value stored in it's primary key column, which we can name seller_id.
A simplified version of such a table could look like this:
In a similar manner, the customer table should contain data only applicable to customers. The qualities (attributes) about customers that we wish to store become the columns in the customer table. Each row (record) in the customer table represents an individual customer. Each individual customer is uniquely identified in that table with a unique value in it's primary key column, which we can declare as customer_id.
A simplified version of this table:
I'm guessing the business rules state that any customer is able to request any number of products, from any seller, any number of times...since surely any seller would want as many sales and customers as possible!
How can we express and record the interactions (relationship) between seller and customer?
This is done with a new kind of entity: a composite entity. It becomes a new table, having it's own primary key, and contains seller_id and customer_id as foreign keys. The foreign keys in this table connect (relate) the seller table to the customer table.
We can name this new table quotation (if that is your preferred name). Each row of this table is intended to capture and record each and every individual transaction between a customer and a seller. The columns (attributes) of this table are the data that apply to a transaction between a customer and seller, such as amount or date of sale.
A very simplified version of this composite entity:
Note that the foreign key values that exist in this table must already exist in their respective tables as a primary key value. That is, a foreign key value cannot be entered into this table unless it exists already as a primary key value in it's own table. This is important, and it is called referential integrity - it ensures that there is no record of a customer purchasing from a non-existent seller, etc.
In the example above we can see that Builder B requested a quotation from Acme Construction in the amount of $3500.00. They then requested another quotation at another time for the amount of $1800.00. What else does it reveal? All existing customers have ordered something. Acme Lumber has not made a sale at all (yet), etc.
A design such as this enables the database to store any number of transactions between sellers and customers. Likewise, it supports the addition of any number of new customers and sellers, even if they have not sold or purchased anything yet. Queries can be run that reveal which sellers have sold the most or least, and so on.
Good luck with your studies!
Is it possible to have the ID of the next generated row (across 2 tables) be unique?
I have 4 tables:
1 for teachers
1 for students
1 for projects
1 for relations
The relations table has 3 foreign keys.
One refers to teachers IDs, one to students IDs and the other to projects IDs
Since a project can be related to teachers but also students at the same time, how do I make sure that a new created teacher or student won't have an ID already used by the other type of account?
If I can do that, then the relations table would have only 3 columns:
ID, project_ID and related_to(ID)
If not, I would have to add a 4th row indicating the type of account that it relates to (student or teacher).
Thanks for your help!
Regarding the difference between account types:
I have to translate this exact same situation to another project of mine in which the first two tables are completely different. That's why I don't bother to merge the students and teachers tables here.
You do not need to have unique values between the student and teacher tables because the relation table has separate fields for each relationship, so there is no conflict.
However, this is not the right way to do things. You need two relation tables, teacher_project and student_project. Alternatively, depending on the unique data that's different between teachers and students, you could have a single person table and a single relationship, which is probably closer to the real world anyway.
I think you can identify the teachers begin with 1 ,incremental 2; the students begin with 2 ,incremental 2.By this way,odd number refers to teacher while even number refers to student.No conflict will happen.