I have a table of transactions. For any given record, I want to be able to include a portal which shows all related transactions. Since the related records are in the same table as the parent record, I have created a second table occurrence (TO). I have linked these two TOs with a join table, into which I enter the foreign keys of the two TOs to indicate which records relate to which other records.
On the layout for a given transaction, I've added a portal which displays related records from the second table occurrence. So far, so good.
So, let's say in the join table I said transaction 100 is linked to transactions 105 and 110. In the portal for transaction 100, I can see records 105 & 110.
However, I would also like to see transaction 100 in the portal for transaction 105, but can't figure out how to do this, without having to manually enter the same relationship, but in reverse.
NB. I'm using Filemaker Pro 12.
You need to create two records for each relationship in the intermediate table to do this.
For example, you have TO_1 and TO_2 and an intermediate table. The intermediate table has two fields, id_1 and id_2. When you create a relationship between TO_1 and TO_2, create two records in the intermediate table. One record stores the id of TO_1 in id_1 and TO_2 in id_2. The second record stores the id of TO_1 in id_2 and TO_2 in id_1.
It sounds like you want all the foreign keys to be present in a single field that you use a multi-key. In your example, the multi-key would look like this:
100
105
110
If you do not want to display the present record in a portal of related records, you can omit it be defining the relationship to exclude itself by adding the predicate something like this:
fk = fk AND
pk ≠pk
Would that work?
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 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.)
I have the following situation. The entries in a table come from a list of users for a particular id. That way id 7 has 3 rows for, say, 2, 6, 7 (these three are unique ids for a user data table). To clarify the table looks like this.
ID USERID KEYID
Where KeyID is auto_inc and is the table's primary key.
These entries come from a multiple select field. So a user might want to delete user 2 and add user 8. So the function that needs to update the table gets the array 8,6,7 for id 7. The quick way I found to do the syncronization is simply to delete every entry in the table for ID 7 and add 3 new entries of the from (ID,USERID) (7,8) (7,6) (7,7).
However I don't know if this is how it's supposed to be. Is there a better way? Also this methods drives the keyid up really fast (for every modification in the table, basically). Is that a problem? I'm an newbie with these things, so please be patient.
Well, you can delete rows selectively like this:
DELETE FROM my_table WHERE user1 = 7 AND user2 NOT IN (8,6,7)
where (8,6,7) is list of pairs (7,6),(7,8),(7,7) , that should be preserved, kept, not deleted, and it will delete all other pairs (7,?)
Your next question may be "Then how to add pairs while not making duplicities?"
You will first need to teach your table what duplicity is. By adding unique key on pair of fields (user1,user2). That would forbid duplicities. Now, when inserting new rows that may be already there, use "INSERT IGNORE" to ignore such exception and simply, continue on.
I know it's possible to have n amount of columns, but is it proper mysql "coding standard"?
Here is what I'm doing:
I am a table student which includes all the students info including testScores:
student
-------
studId
name
age
gender
testId
Instead of putting each individual test answer within the student table, I made a separate table called testAnswers that will hold each students test results:
testAnswers
-----------
testId
ques1
ques2
.
.
.
quesN
Each entry in the testAnswers table corresponds to a specific student in the table student.
Of course, there will be an admin that will be able to add questions and remove questions as each year the test questions may change. So, if the admin were to remove an answer, than that means one of the columns would be removed.
Just to reiterate myself, I know this is possible to edit and remove columns in a table in mysql, but is good "coding standard"?
The answer is a simple and clear: No. That's just not how you should do it except for very few corner cases.
The usual way to approach this is to normalize your database. Normalization follows a standard procedure that (among other things) avoids having a table with columns names ques1, ques2, ques3 ....
This process will lead you to a database with three tables:
students - id, name, and other stuff that applies to one student each
questions - id and question text for each question
answers - this is a N:M relation between students: student_id, question_id, answer_value
Use two tables!
What you are describing is a one to many relationship as there can be one student to many test scores. You would need to have some id as a foreign key to the student_id and put this id in the testAnswers table. You can then set constraints, which tell the database how to handle removal of data.
As one commenter has mentioned, using one table would result in breaking 1nf or first normal form which basically says that you cannot have multiple values for a single column given a particular record - You can't have multiple test scores for the same user in a given table, instead break the data up into two tables.
...of course 2 tables, also could use 3, just remember to insert a studId column also in the testAnswers table (with REFERENCE to the student table) and an INNER JOIN testAnswers ON student.studId=testAnswers.studId at the SELECT query (to read the data).
I have a table for many-to-many relationship of users (three columns: relationship_id, user_id, user_id). How can I keep the relationships unique when the table accepts any entry? When I have a row of
22 11 43
How can I prevent INSERT of next_id 11 43 and more importantly next_id 43 11? When user 11 requested relationship with user 43, user 43 must not be able to request relationship with user 11.
How can I check two columns before INSERT?
And my problem is even more serious as I have two tables (request and relationships). A row from request table will be deleted and inserted into relationships upon user approval. The reason for using two tables is that many pending requests make the table so long, which should be used regularly for displaying user friends.
When INSERTing request from user 11 to user 43, what is the fastest and efficient method to check for possible existence of 11 43 and 43 11 rows in tables: requests and relationships?
Anytime I have used a "Linking Table" to keep track of many to many relationships I always DELETE any existing relationships before INSERTING the new relationships. However, this may not work in your case because your linking table contains the surrogate key relationship_id. If you drop the surrogate key from the linking table and use a stored procedure you can do every thing you listed.
Identifying DuplicatesCreate a View using CASE logic
CREATE VIEW vFriendRequests
AS
SELECT
CASE
WHEN ID_1 < ID_2 THEN ID_1
ELSE ID_2
END CASE as RequestId_1,
CASE
WHEN ID_1 < ID_2 THEN ID_2
ELSE ID_1
END CASE as RequestId_2
FROM Friend_Requests_Table
Then you can do a select distinct from this view to get only the unique sets of requests.
Here are some options to achieve what you want (which to choose or combine depends mainly on your datamodel, client architecture and storage engine):
create a unique composite index on both user_id columns
revoke INSERT into relationships and implement a Stored Procedure for INSERT (this can do any checks etc. you want) OR implement an ON BEFORE INSERT trigger which does what you want
IF the the order of the user_ids is not relevant change the INSERT code to always sort both IDs before INSERTing (for example via the Stored Procedure approach)
This way you don't need to check explicitely but the index will do all work for you
create a fourth column idcomb in relationships with a UNIQUE INDEX and an ON BEFORE INSERT TRIGGER which just takes both user_id sorts them and concatenates them with a - inbetween and assign that to idcomb column as value... this way all work is done by the index and no change on the client-side is needed (when some duplicate is inserted is just comes back with an error)