I have records table with booking records info (8 columns). And I want to add to a record information about extra services that a client booked. I created extra_services table, but how can I specify multiple extra services to one record in records table?
If I add 9th column with just one id of extra service then there will be redundancy problem.
It depends a little on what is the content of the extra_services table. If it does contain a set of extra services that can be booked you need a table to cross reference the bookings with the extra_services.
If on the other hand you are storing the booked extra services belonging to the record you can just use a ForeignKey field to the index of the records table in the extra_services table, that way you can track which records in extra_services belong the booking record.
Related
I am going to write some code to retrieve and add to/remove from a student's hours that they have signed up for. For example...
student 1:
October 20th:
12am
4pm
7pm
October 21st:
8pm
student 2
October 19th
1pm
6pm
I'm trying to wrap my head around how to create this type of table setup on phpmyadmin with each student having a dynamic number of hours, and different times, and different days. I am new to mysql management, am vaguely familiar with joins and stuff, and am just now starting to expand my database to more complex things like this. What I have learned so far is that enums is NOT where I want to go. Just unsure of a starting point...
What is a good strategy for doing something like this?
Thank you,
you need to create many to many relation
first i try to explain it simple and fast:
1- you need to make a table for hours, each hours have 1 row.
2- i guess you already have a student table
3- now you need a table that contain only 2 column, first column is hours table id, second column is student id.
at the end you simply need to execute select command like this:
select * from StudentHours Table where student-id = 1;
Detailed Information:
Relational database systems usually don't allow you to implement a direct many-to-many relationship between two tables. Consider the example of keeping track of invoices. If there were many invoices with the same invoice number and one of your customers inquired about that invoice number, you wouldn't know which number they were referring to. This is one reason for assigning a unique value to each invoice.
To avoid this problem, you can break the many-to-many relationship into two one-to-many relationships by using a third table, called a join table. Each record in a join table includes a match field that contains the value of the primary keys of the two tables it joins. (In the join table, these match fields are foreign keys.) These foreign key fields are populated with data as records in the join table are created from either table it joins.
A typical example of a many-to many relationship is one between students and classes. A student can register for many classes, and a class can include many students.
The following example includes a Students table, which contains a record for each student, and a Classes table, which contains a record for each class. A join table, Enrollments, creates two one-to-many relationships—one between each of the two tables.
I have a database with the following table.
Entity (ID, EntityType),
Tickets (TicketId, ..., (TicketId refers Entity (ID)),
Contacts (ContactId, ..., (ContactId refers Entity (ID)).
I want to duplicate Ticket data in another table,
TicketsDup (TicketID, ...).
In TicketsDup table TicketID should refer Entity table or Tickets table?
The point of TicketsDup is to store only active tickets. So inactive tickets will be deleted from TicketsDup table. But will still be stored in Tickets Table. The user can mark a ticket as active. In which case the ticket has to be inserted into TicketsDup table. Also modified time has to be updated in Tickets table. This is where my concern is. Mysql locks parent rows from getting updated when a child row is being inserted. This causes deadlock. Is it wrong to refer Entity table for TicketsDup table? I hope the question is not vague.
I would suggest to write every new ticket to the STORE table and then duplicate it in the ACTIVE table. So you don't get any problems with the id field.
If the ticket in the ACTIVE table is closed you copy the data into the STORE table and remove it from the active table.
If you search for an ticket you search the ACTIVE table first and then in the STORE table.
If a ticket in the STORE table is marked for active you copy it back to the ACTIVE table.
But if you don't have that many tickets I would stick to one table only. I have 6 years of tickets in one table and its not getting slower. Just mark them active and nonactive. I don't even delete a ticket just mark it deleted.
I am importing data from excel file to MySQL ,using php MyAdmin as tool manager through PHP. It's a printer report where every user have an unique user_id but can make many registers per day what I want is relate one table which contains the user's id and the registers per day and in another table I have information about cost center of each user, what I want to query is the top of users that make more registers per month but not printing the users itself (the info contained on the first table) but the cost center of that users contained on the second table, etc, if on the first table there is an unique ID per activity it is possible relate to the second table which also contains the users ( user_id ) and center cost?
Let's say I have a database table called products which has a list of products, with the primary key product_id
I then have a database table called purchase_order_products which has a list of products assigned to a purchase order, with a foreign key product_id.
Now, if I enforce referential integrity between the two tables, it only requires a single purchase order to reference a product, and it won't be possible to ever delete that particular product from the database (unless the purchase orders for that product are also deleted).
It seems I have a few options:
1) Enforce referential integrity and don't allow the product to ever be deleted.
2) Don't enforce referential integrity, and if anyone ever views a purchase order where the product no longer exists, simply display the product name as "UNKNOWN" or "DELETED".
3) The final option is to not only store the product name in the products table but also store it in the purchase_order_products table alongside the foreign key. Obviously this is redundant data, but it would allow the product to be deleted from the products table, whilst still allowing users to see the names of now non-existent products that were part of purchase orders in the past.
I'm swaying towards option #3 but wondered what is the "correct" way of handling this.
You can enforce referential integrity and use ON DELETE SET NULL, then display "UNKNOWN" or "DELETED" when a purchase order's product_id is null. Thus, option 1 and 2 aren't mutually exclusive.
Option 3 is valid. Having two copies of product_name isn't redundant if the relations they're used in express different predicates. Product <x>'s current name is <y> is different from When purchase_order <z> was created, product <x>'s name was <y>. It's a common technique to record current and historical prices separately, the same can be done for names or any other attributes of a product.
There is no reason to duplicate data. A simple solution is to implement a soft delete on the products. The best way is to have a date field called something appropriate like Deleted and set it to a date far in the future, like 12/31/9999, for current products. To delete a product, just set the Deleted value to the date the product is deleted. This way, to list currently available products, filter out the products where Deleted is in the past.
When showing purchase orders, ignore the Deleted value so it shows all products, even the ones no longer available. Optionally, you could show by some indicator if a product is one that is no longer available.
You might also want to create a view that ignores deleted products for those times in would not be appropriate to show deleted products, as when creating new purchase orders.
You would also want to write a delete trigger on the products table to convert the delete process to just change the value in the Deleted field. You would also want to have a function in the API to allow a product to be "deleted" as of a certain date. Maybe the product was removed a month ago but the database was not updated. Or the product is slated to be removed at a future date so go ahead and set the date. The product will simply disappear from the current products view when that date is reached.
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!