Problem:
A student has mother, father, elder sister and elder brother. If the student's parents occupation is teacher, the I want to generate tree in UI by getting data from backend table. For this, I have created a table to store student information like, student id(pk), name of student, gender, address, father,mother, father_occupation, mother_occupation, etc., Also I added one option (checkbox) in UI to find student's relative occupation is teacher or not. If checkbox is true, then occupation column will be update a value true or 1.
For this, one table is enough or more than one table needed? Also how the query should if all in one table and how the query should be if need to maintain in separate tables.
You have a bunch of options for this schema, but for future scale, I would go with a hierarchy type table, and then attribute table(s) for the folks involved in the hierarchy. This would allow you to track student/teacher relationships (with the right attributes) within the same structure.
Table1 would hold your hierarchical information, which would be the relationships between your people:
id | parent_id | other_relationship_attributes
Table2 would hold information about the individual:
id | occupation | gender | etc..
You can then write queries that can traverse your hierarchy and pull relevant info from the individuals table.
If your student info is very different then your parent info (probably), then that second table would make sense to break up into two tables. 1 for your student and one for the parents.
An example of what this might look like in SQL, answering the question "Show me all students where their parents are teachers:
SELECT
student.id,
student.name,
CASE WHEN student.gender = 'F' THEN 'Daughter' ELSE 'Son' END as child_relationship
parent.id,
parent.name,
parent.occupation,
CASE WHEN parent.gender = 'M' Then 'Father' ELSE 'Mother End as parent_relationship
FROM
person as student
INNER JOIN hier on student.id = hier.id
INNER JOIN person as parent on hier.parent_id = parent.id
WHERE
parent.occupation = 'Teacher'
Related
I'm trying to find out which schools had students that did not complete their exams in 2018. So I've got 3 tables set up being: ExamInfo, ExamEntry and Students. I'm going to try use the ExamInfo table to get information from the Students table though, I obviously only want the student information that did not complete their exam in 2018. Note: I'm looking for students that attended, though did not complete the exam, with this particular exam you can look at completed exam as passed exam.
Within ExamInfo I have the columns:
ExamInfo_Date --when exam took place, using to get year() condition
ExamInfo_ExamNo --unique student exam ID used to connect with other tables
ExamInfo_Completed --1 if completed, 0 if not.
...
Within ExamEntry I have the related columns:
ExamEntry_ExamNo --connected to ExamInfo table
ExamEntry_StudentId --unique studentId used to connect to Students table
ExamEntry_Date -- this is same as ExamInfo_Date if any relevance.
...
Within Students I have following columns:
Students_Id --this is related to ExamEntry_StudentId, PRIMARY KEY
Students_School --this is the school of which I wish to be my output.
...
I want my output to simply be a list of all schools that had students that did not complete their exams in 2018. Though my issue is with getting from the ExamInfo table, to finding the schools of which students did not complete their exam.
So far I've:
SELECT a.Students_School, YEAR(l.ExamInfo_Date), l.ExamInfo_Completed
FROM ExamInfo l ??JOIN?? Students a
WHERE YEAR(l.ExamInfo_Date) = 2018
AND l.ExamInfo_Completed = 0
;
I'm not even sure if going through the ExamEntry table is necessary. I'm sure I'm meant to use a join, though unsure of how to appropriately use it. Also, with my 3 different SELECT columns, I only wish for Students_School column to be output:
Students_School
---------------
Applederry
Barnet Boys
...
Clearly, you need a JOIN -- two in fact. Your table has exams, students, and a junction/association table that represents the many-to-many relationship between these entities.
So, I would expect the FROM clause to look like:
FROM ExamInfo e JOIN
ExamEntry ee
ON ee.ExamEntry_ExamNo = e.ExamNo JOIN
Students s
ON ee.ExamEntry_StudentId = s.Students_Id
Assuming only one school can be identified in a specific town, you are required to move students from duplicated schools to originally created schools. We also assume that lowest school id implies the first schools to be created in
the database, hence original schools.
I want to achieve this simply by changing the school ids for duplicate school+town to the smallest school id (the original) in that category. This will take care of the student records table that is linked to this one via foreign key (school id).
How would I go about doing this on the table attached? I'm thinking along the lines of SELECT MIN, CASE STATEMENTS as well as GROUP BY and COUNT() but I'm at a loss on how to combine these. Anyone have an idea/code on how I would achieve the requirement above?
I'd assume that the school id is a unique identifier (key). Therefore you can't just update it in the schools table. You'd rather need to update the school_id column in the students table to point to the original school's id.
If this is the case you can do something along the lines of
-- get all students and their current school info for update
UPDATE students st JOIN schools sc
ON st.school_id = sc.id JOIN (
-- get ids of original schools
SELECT town, name, MIN(id) id
FROM schools
GROUP BY town, name
) q -- join students with a list original schools ids
ON sc.town = q.town AND sc.name = q.name
-- change the school id to the original one
SET st.school_id = q.id
-- but only for students that were associated with non-original schools
WHERE st.school_id <> q.id
Here is dbfiddle demo
Considering this ER diagram
we have Students who are admitted to participate in an Exam, and each Exam can be split up into multiple Runs (for example, to split up large groups across multiple rooms or to have two Runs for the same Exam in direct succession).
Is it possible to ensure (via database constraints) that Students participate only in Runs that belong to Exams they are admitted to?
I couldn't find a way on my own and also don't know how to phrase this for an internet search.
You have these tables and columns:
exam: id, name
student: id, name
run: id, exam_id (foreign key to exam.id), when (timestamp), room
You need a new intersection table to keep track of what exam is being taken by which student:
int_exam_to_student: exam_id, student_id - both foreign keys
Now, you can query this to determine what runs a student is allowed to be in:
select run.* from run join int_exam_to_student i on (run.exam_id = i.exam_id) where i.student_id = 123;
Ok, so I am going to try and be specific as possible but my MySQL skills are pretty weak. So here is the situation:
I have 2 tables: Donor and Students. A donor can be linked to as many students as they want and each student can be linked to as many donors as donors want to "claim" them. So if I have Sally, a student, she can have Jim, a donor, and Jeff, a donor, be linked to her. So, I have all my students in one table and all my donors in another table. I need to put them together show the students name, id and the id of all the donors that the student is linked to.
Currently my tables are: Donor with DonorID, FirstName, LastName, DonorType, StreetAddress, etc. Then Students with: StudentID, FirstName, LastName and DonorID. However, that only allows me to link a student with one donor. So, I was thinking I need to make a transition table that would allow me to show the StudentID, FirstName(of student), LastName(of student), and the DonorID that "claims" that student and allow for me to duplicate StudentID and put a different DonorID in the 2nd, 3rd, 4th, so on and so on entries of the same student.
So, I guess my question is how do transition tables work in MySQL; I believe I am going to need to work with the JOIN function and join the two tables together but after reading about that on tizag.com I am even more confused. I have worked with Access where when you create a transition table you can pull the PK from each table and create a composite key using the two keys from the other tables but I am not quite sure how to do that in MySQL; does it work essentially the same and I should be pulling the PK from each table and linking them together in the 3rd, transition, table?
Marvin's right.
You need three tables to pull this off.
Donor
DonorID
FirstName
LastName
DonorType
StreetAddress
etc.
Student
StudentID
FirstName
LastName
etc.
Then you need Student_Donor. This is often called a join table, and implements the many-to-many relationship.
StudentID (PK) (FK to Student)
DonorID (PK) (FK to Donor)
DonorOrdinal
If StudentID = 5 has four donors with ID = 6,7,11,15, then you'l have these rows
StudentId DonorId DonorOrdinal
5 6 1
5 7 2
5 11 3
5 15 4
The DonorOrdinal column allows you to specify a student's primary donor and secondary donors. I can't tell from your question how important that is, but it's helpful to be able to order these things. Remember this: formally speaking, a SQL SELECT query returns rows in an unpredictable order unless you also specify ORDER BY.
If you want to display your students and their donors, you'll need this query:
SELECT s.StudentID, s.FirstName, s.LastName,
sd.DonorOrdinal,
d.DonorType, d.DonorID, d.FirstName, d.LastName
FROM student s
LEFT JOIN student_donor sd ON s.StudentID = sd.StudentID
LEFT JOIN donor d ON sd.DonorID = d.DonorID
ORDER BY s.StudentID, sd.DonorOrdinal, d.DonorID
This will show you all students (whether having donors or not per LEFT JOIN) in order of ID, then their donors in order of DonorOrdinal.
Yes, pretty much. What you are talking about is a Many to Many relationship. Your donor table should not include a reference to the student table (and vice versa). You'll need a new table (what you are calling a transition table) that contains the DonorId and StudentId. This can comprise your primary key or you can use another column for the primary key that is an auto_increment.
i need to specify following in one query: It should include the Activity_name and Child_ first_name and last_name for each child registered for the specified Activity. There is (Football/Art/IT) activities in Activity Table(which has primary_key for each activity). What would be the query that would list children registered for Art activity? Children name's should be displayed in one column. Thanks.
Without providing your table structure, I cannot provide an accurate query.
However, if I were to design a set of tables that store a list of children, a list of activities, and a correlation between the two, it would consist of three tables named "children," "activities," and "linktable" in this example.
children
id
first_name
last_name
activities
id
name
linktable
child_id
activity_id
children stores the names and information of every child, and a unique id. activities stores the names and relevant information about activities, as well as a unique id. Finallly, linktable may be something like "schedule" or "signups" in your system, and should link children to activities and allow for what is called a many-to-many relationship. In other words, one child may participate in many activities, and any activity may be engaged by many children.
The following query is an example of how to see which children are signed up for Art:
SELECT
a.name, CONCAT(c.first_name, ' ', c.last_name) AS child_name
FROM
children c, activities a, linktable
WHERE
linktable.child_id = c.id
AND
linktable.activity_id = a.id
AND
a.name = 'Art';