i have gotten the task of creating a statistic from tables that look like this:
Faculty
1 FacultyName1
2 FacultyName2
3 FacultyName3
4 FacultyName4
5 FacultyName5
and this:
Student
1 StudentName1 FacultyNr2
2 StudentName2 FacultyNr3
3 StudentName3 FacultyNr5
4 StudentName4 FacultyNr2
now i have to create a statistic which Groups the Faculties into newly created fields and groups by them.
Say:
Faculty Group 1 Count: 3
Faculty Group 2 Count: 1
for this example lets say that all those of FacultyName1,FacultyName2,FacultyName3 should be listet as of "Faculty Group 1" and FacultyName4 and FacultyName5 as of "Faculty Group 2".
I started by doing the following:
Select Count(*)
FROM Student INNER JOIN Faculty on Student.FacultyID = Faculty.ID
But am stuck trying to understand how to Group, how i could create Groups in the Code, where i could just say: Group by FacultyGroups (Select Case When FacultyName = 'FacultyName1' = 'Faculty Group 1')
or something similiar, does anybody have any idea ?
Assuming that you have added a GroupID column in your Faculty table
SELECT COUNT(*), f.GroupID
FROM Student AS s
INNER JOIN Faculty AS f ON s.FacultyID = f.ID
GROUP BY f.GroupID
It gives you the number of student per group of faculties and the id of this group
There are better ways, but this should work:
SELECT
CASE
WHEN f.Name IN ('FacultyName1', 'FacultyName2', 'FacultyName3') THEN 'FacultyGroup1'
WHEN f.Name IN ('FacultyName4', 'FacultyName5') THEN 'FacultyGroup2'
END AS FacultyGroup,
COUNT(*) AS Students
FROM
Student s
INNER JOIN Faculty f ON s.FacultyID = f.ID
GROUP BY
CASE
WHEN f.Name IN ('FacultyName1', 'FacultyName2', 'FacultyName3') THEN 'FacultyGroup1'
WHEN f.Name IN ('FacultyName4', 'FacultyName5') THEN 'FacultyGroup2'
END;
If your "group" logic becomes too long then it will look messy in your query, so you might want to pre-calculate this. You could do this by using a sub-query for example, so one part of your query (the sub query) would convert faculties to groups and the other "main" part would count the students per group.
Related
I need to make one SQL command.
From table with comments i'll get comment id, then
with this ID I need to get count of reactions with the same comment ID and user's names.
So for example I have this 2 tables:
Comments:
ID
Comm_text
1
Example text
2
Another example
and Reactions:
ID
comm_id
usr
etc..
1
1
Peter
another
2
1
John
collon
3
1
Dog
cuz
4
2
Cat
why not
I need to get this:
ID
Comm_text
Reactions_Count
Users
1
Example text
3
Peter, John, Dog
2
Another example
1
Cat
I tried this:
SELECT k.id, k.comm, COUNT(r.id) as reactions, r.usr
FROM `comms` k
INNER JOIN `reactions` r ON r.id=k.id
It's just one row with one comment and count of all rows in reaction table.
Thanks.
Try this query that makes the same output:
select comments.id as ID , comments.Comm_text as Comm_text ,
(select count(id) from Reactions where comm_id = comments.id) as Reactions_Count ,
(select coalesce(GROUP_CONCAT(usr ORDER BY usr DESC) , '') from Reactions WHERE comm_id = comments.id) as Users
from comments group by comments.id
You should use group by to group the comments and have just one row then use query to count and gather the data, based on each row of the group.
The GROUP_CONCAT attach the output with , and the coalesce set the output to a given string if the output was empty.
Read more about:
GROUP BY
GROUP_CONCAT
COALESCE
subquery
According to the names that u set in the example, this will work. Just fix the table names for your database structure.
SELECT `Comments`.`ID`, `Comments`.`Comm_text`, count(`Reactions`.`comm_id`) as react, `Reactions`.`usr`
FROM `Comments`
INNER JOIN `Reactions`
ON `Comments`.`ID`=`Reactions`.`comm_id`
GROUP BY `Reactions`.`comm_id`
I have a relation between users and groups. Users can be in a group or not.
EDIT : Added some stuff to the model to make it more convenient.
Let's say I have a rule to add users in a group considering it has a specific town, and a custom metadata like age 18).
Curently, I do that to know which users I have to add in the group of the people living in Paris who are 18:
SELECT user.id AS 'id'
FROM user
LEFT JOIN
(
SELECT user_id
FROM user_has_role_group
WHERE role_group_id = 1 -- Group for Paris
)
AS T1
ON user.id = T1.user_id
WHERE
(
user.town = 'Paris' AND JSON_EXTRACT('custom_metadata', '$.age') = 18
)
AND T1.user_id IS NULL
It works & gives me the IDs of the users to insert in group.
But when I have 50 groups to proceed, like for 50 town or various ages, it forces me to do 50 requests, it's very slow and not efficient for my Database.
How could I generate a result for each group ?
Something like :
role_group_id user_to_add
1 1
1 2
2 1
2 3
The only way I know to do that for now is to do an UNION on several sub queries like the one above, but of course it's very slow.
Note that the custom_metadata field is a user defined field. I can't create specific columns or tables.
Thanks a lot for your help.
if I good understood you:
select user.id, grp.id
from user, role_group grp
where (user.id, grp.id) not in (select user_id, role_group_id from user_has_role_group) and user.town in ('Paris', 'Warsav')
that code give list of users and group which they not belong from one of towns..
To add the missing entries to user_has_role_group, you might want to have some mapping between those town names and their group_id's.
The example below is just using a subquery with unions for that.
But you could replace that with a select from a table.
Maybe even from role_group, if those names correlate with the user town names.
insert into user_has_role_group (user_id, group_id)
select u.user_id, g.group_id
from user u
join (
select 'Paris' as name, 1 as group_id union all
select 'Rome', 2
-- add more towns here
) g on (u.town = g.name)
left join user_has_role_group ug
on (ug.user_id = u.user_id and ug.role_group_id = g.group_id)
where u.town in ('Paris','Rome') -- add more towns here
and json_extract(u.custom_metadata, '$.age') = 18
and ug.id is null;
I am having a major problem joining 5 tables because each table only has 1 column in common with only 1 other table.
Here are my tables and columns in each table:
TABLE (COLUMNS)
person (person_id, first_name, last name)
building (building_id, building_name)
room (room_id, room_number, building_id, capacity)
meeting (meeting_id, room_id, meeting_start, meeting_end)
person_meeting (person_id, meeting_id)
OK, now here is what I am trying to do (pasted from a homework assignment):
Construct the SQL statement to find all the meetings that person_id #1 has to attend. Display the following columns:
Person’s first name
Person’s last name
Building name
Room number
Meeting start date and time
Meeting end date and time
Now I know how to join 2 tables but I have no idea how to pull info from 5 different tables like this.
I tried looking up how to do this and it just says to do a UNION command, and I am just learning and have yet to cover that.
As UNION is used to combine the result from multiple SELECT statements into a single result set, you don't need it for this scenario. You have to join all the tables one by one based on their Id.
SELECT P.First_Name, P.Last_Name, B.Building_name, R.Room_Number,
M.Meeting_Start, M.Meeting_End FROM Person P
JOIN Person_Meeting PM ON P.Person_Id = PM.Person_Id
JOIN Meeting M ON PM.Meeting_Id = M.Meeting_Id
JOIN Room R ON M.Room_Id = R.Room_Id
JOIN Building B ON R.Building_Id = B.Building_Id
WHERE P.Person_Id = 1
I found one question in MySQL I am trying. Please tell me if following solution will work or is there any better solution?
select D.DEPT_NAME, COUNT(*)
from Departments D
left outer join STUDENTS S
on S.Dept_ID = D.Dept_ID
group by D.DEPT_NAME
order by 2 desc, 1
Students table has following fields:
Student_ID
Student_Name
Gender
Dept_ID
Departments table has following fields:
Dept_ID
Dept_Name
A university uses 2 data tables, Students and Departments, to store data
about its students and the departments associated with each major.
Write a query to print the respective department name and number of students
majoring in each department for all departments in the Departments table
(even ones with no current students).
Sort your results by descending number of students; if two or more departments have same number of students, then sort those departments alphabetically by department name.
Forgive me altering the formatting of the code.
I would change the ORDER BY, as follows:
SELECT
d.DEPT_NAME,
COUNT(s.STUDENT_ID)
FROM
Departments d
LEFT JOIN Students s ON d.DEPT_ID = s.DEPT_ID
GROUP by
d.DEPT_ID
ORDER by
COUNT(s.STUDENT_ID) DESC,
d.DEPT_NAME ASC
You need a way to count the students in each department, then you need a way to list all departments, even those without students.
Counting the students in each department: (http://sqlfiddle.com/#!15/39a8b/15/0)
SELECT Dept_ID, COUNT(*) Students
FROM STUDENTS
GROUP BY Dept_ID
Then, treating that as a subquery, left join it to your other table. (http://sqlfiddle.com/#!15/39a8b/16/0)
SELECT D.DEPT_NAME, S.Students
FROM Departments D
LEFT JOIN (
SELECT Dept_ID, COUNT(*) Students
FROM STUDENTS
GROUP BY Dept_ID
) S ON D.Dept_ID = S.Dept_ID
The LEFT JOIN preserves rows in the DEPARTMENTS table that don't match the ON clause. This gets you stuff like this.
Biology 7
Mathematics (NULL)
Sociology 11
Physics 3
So you have to deal with that (NULL) problem. Here's how. Change the SELECT to say
SELECT D.DEPT_NAME, IFNULL(S.Students,0)
It's a little tricky to join a table to an aggregate where the aggregate (the COUNT/GROUP BY query) has missing data. But that's how you do it.
You can figure out the ORDER BY stuff on your own.
SELECT d.department_name, COUNT(s.student_name) AS student_count
FROM student s
LEFT JOIN department d
ON s.department_id = d.department_id
GROUP BY department_name
ORDER BY d.department_name;
!!This is finally the correct answer !!
Don't hardcode the problem please stay tuned and work like professional
Excute below.
SELECT
ad.Dept_Name,
count(ass.Student_Id) as Stduent_Enrolled
FROM [Alok.Departments] ad
Left Outer Join [Alok.Students] ass
ON ad.Dept_ID = ass.Dept_ID
Group by ad.Dept_Name
ORDER by
CASE WHEN COUNT(ad.Dept_ID) >=2
THEN ad.DEPT_NAME END desc,
CASE WHEN COUNT(ad.Dept_ID) < 2
THEN ad.DEPT_NAME END asc
1 select department_name, count(student_id) as student_count
2 from student
3 left outer join department ON
4 department.department_id=student.department_id
5 group by department_name
6 order by department_name;
#jaat
Use this query
select count(*) from tblstud_info s,tbldept d where s.dno=d.dno group by d.dname
I am using SQL Server 2008 and I have 4 tables StudentAbsentees, Students, StudentSections and Sections
In the StudentAbsentees table I am storing the studentId that are absent (absentees only) on a particular day like,
StudentId Time Date
----------- ------ ------
1 10:00 2012-04-13
and in the StudentSections I am storing the studentId in a particular section like
StudentId SectionId
---------- ------------
1 1
2 1
3 1
and in the Students table I am storing student details, likewise in Sections table I have section details like name and capacity of that section.
I need to join these tables and display whether the student is present/absent on a particular day... the result should be
StudentId Status
--------- ------
1 Absent
2 Present
3 Present
I can get the absentees list from these tables, I dunno how to display whether they are present/absent....can anyone help me here
select * from (
select s.id,
case
when sa.date = '2012-01-01'
then 'absent'
else 'present'
end as status,
ROW_NUMBER() OVER (PARTITION BY s.id ORDER BY CASE WHEN sa.date = '2012-01-01' THEN 1 ELSE 2 END) AS RowNumber
from students s
left outer join studentabsentees sa on s.id = sa.studentid
)
as a where a.RowNumber = 1
You're query to show the status of all students for a particular day would look like:
select s.id, s.name, a.status
from student s
left join studentabsentees a on s.id = a.studentid
where a.date = ?
Obviously you have to supply a date.
Note: Your question uses "inner join" in the title. I think left is a better fit because it would show for all students. But if you really wanted just the ones that have a record in the absentee table then you could just change the word "left" in the query to "inner".
Note2: My query assumes a status field. If you don't have one then look at juergen d's answer.
No need for joins, you can just use set operators:
SELECT StudentID, 'Absent'
FROM StudentsAbsentees
WHERE [date] = ...
UNION
(
SELECT StudentID, 'Present'
FROM Students
EXCEPT
SELECT StudentID, 'Present'
FROM StudentsAbsentees
WHERE [date] = ...
)
You can display 'Present' and 'Absent' by just selecting them as constant. It's easy to get the list of all the absent students. Then union this with all the present students. Present students are found by taking the complete student list and using the except operator on the missing students. But in this except part make sure you select the absent students as present so they subtract nicely from the list of all students with present next to their name that you have just created.