How can I select both values at once? For example, I have a Lesson that have Students and each Student is linked to a Client, so what I want to achieve is something like:
SELECT l.id,
l.value * clientStudents/totalStudents as total
FROM Lesson l
JOIN lesson_student ls ON l.id = ls.lesson_id
JOIN Student s ON ls.student_id = s.id
JOIN Client c ON s.client_id = c.id
**WHERE c.id = <SOME_CLIENT>**
being clientStudents the count using the WHERE clause and totalStudents without using it.
You can move the condition in the calculation phase. Something like:
SELECT l.id,
l.value * SUM(if(c.id = <SOME_CLIENT>,clientStudents,0)) / SUM(totalStudents) as total
FROM Lesson l
JOIN lesson_student ls ON l.id = ls.lesson_id
JOIN Student s ON ls.student_id = s.id
JOIN Client c ON s.client_id = c.id
GROUP BY l.id, l.value
Related
I am trying to fetch all record that are not related to a certain member,
registration is an intersection entity that solves the many to many for members to lessons.
SELECT * FROM lesson
INNER JOIN training
ON training.id = lesson.training_id
WHERE lesson.id
NOT IN (SELECT registration.lesson_id FROM registration WHERE registration.member_id = 42)
I have been trying to convert this code to use a join statement but for I just can't get it to work.
SELECT l.*
FROM t_left l
LEFT JOIN
t_right r
ON r.value = l.value
WHERE r.value IS NULL
this technique doesn't work since this returns record of lesson that don't have any relation ship at all, I need it to look if it doesn't have a relationship to a specific member.
entity relationships model
You want to turn your NOT IN into an anti join? Why? I find NOT IN much more readable.
Anyway:
SELECT *
FROM lesson l
INNER JOIN training t ON t.id = l.training_id
LEFT JOIN registration r ON r.lesson_id = l.id AND r.member_id = 42
WHERE r.id IS NULL;
I think that you just need to add a join condition on the member that you are looking for:
SELECT l.*
FROM t_left l
LEFT JOIN t_right r ON r.value = l.value and r.member_id = 42
WHERE r.value IS NULL
Or, starting from your other query:
SELECT l.*, t.*
FROM lesson l
INNER JOIN training t ON t.id = l.training_id
INNER JOIN registration r ON r.lesson_id = l.id AND r.member_id = 42
WHERE r.lesson_id IS NULL
The conversion from NOT IN or NOT EXISTs uses LEFT JOIN and a comparison to indicate that the JOIN failed.
That would be:
SELECT *
FROM lesson l INNER JOIN
training t
ON t.id = l.training_id LEFT JOIN
registrations r
ON r.lesson_id = l.id AND r.member_id = 42
WHERE r.lesson_id IS NULL;
Very important: The comparison on member_id needs to go in the ON clause, not the WHERE clause.
I am trying to get a count of the number of logins during a given timeframe, currently my SQL query displays only results that had at least one login, I'd like it to display even those which have zero logins.
Query i'm using:
SELECT c.FullName, COUNT(l.Id)
FROM LoginsTable l JOIN UsersTable u ON u.Email = l.Email JOIN Organisations c ON c.Id = u.OrganisationId
WHERE l.AttemptTime > "2019-10-01" AND l.AttemptTime < "2019-11-01" AND l.Success = 1
GROUP BY c.Name
ORDER BY c.Name ASC;
You have a few issues. Firstly, you either need to use a RIGHT JOIN from LoginsTable or reorder the JOINs to put the JOIN to LoginsTable last and use a LEFT JOIN. Given the nature of your query the latter probably makes more sense.
Secondly, you need to put any conditions on fields from a table which has been LEFT JOINed into the join condition, otherwise MySQL converts the LEFT JOIN into an INNER JOIN (see the manual). Finally, you should GROUP BY the same fields as specified in your SELECT. This should work:
SELECT c.FullName, COUNT(l.Id)
FROM Organisations c
JOIN UsersTable u ON u.OrganisationId = c.Id
LEFT JOIN LoginsTable l ON u.Email = l.Email AND l.AttemptTime > "2019-10-01" AND l.AttemptTime < "2019-11-01" AND l.Success = 1
GROUP BY c.FullName
ORDER BY c.FullName
I found 2 issues here:
your group by column is not listed on your column
date condition is using double quotes.
try below query.
SELECT c.FullName, COUNT(l.Id)
FROM LoginsTable l
LEFT JOIN UsersTable u ON u.Email = l.Email
LEFT JOIN Organisations c ON c.Id = u.OrganisationId
WHERE l.AttemptTime between '2019-10-01' AND '2019-11-01' AND l.Success = 1
GROUP BY c.FullName
ORDER BY c.FullName ASC;
As Roman Hocke said you need to use left join as below :
SELECT c.FullName, COUNT(l.Id)
FROM UsersTable u
JOIN Organisations c ON c.Id = u.OrganisationId
LEFT JOIN LoginsTable l ON u.Email = l.Email
WHERE l.AttemptTime > "2019-10-01" AND l.AttemptTime < "2019-11-01" AND l.Success = 1
GROUP BY c.Name
ORDER BY c.Name ASC;
Moreover, you should fix your group by or select using the same field : SELECT c.Name or GROUP BY c.FullName ORDER BY c.FullName
EDIT : Nick's answer is the one. As he said perfectly well, you need to put your conditions in the on clause of your left join.
SELECT c.FullName, COUNT(l.Id)
FROM UsersTable u
JOIN Organisations c ON c.Id = u.OrganisationId
LEFT JOIN LoginsTable l ON (u.Email = l.Email AND l.AttemptTime > "2019-10-01" AND l.AttemptTime < "2019-11-01" AND l.Success = 1)
GROUP BY c.FullName
ORDER BY c.FullName ASC;
I have a database with the tables:
Student(SID,Name,Surname,Age)
Registration(StudentID,CourseID)
Course(CID,Name,Cost)
I would like to extract only the name of the courses with students younger than 20. Will the query below do just that?
SELECT C.NAME
FROM Course C
INNER JOIN Registration
INNER JOIN Student S
WHERE CID = CourseID
AND SID = StudentID
AND Age < 20
GROUP BY C.NAME
I would also like to extract the number of students in each course having students younger than 20. Is it correct to do it as below?
SELECT count(S.NAME)
,C.NAME
FROM Student S
INNER JOIN Course C
INNER JOIN Registration
WHERE Age < 20
AND CID = CourseID
AND SID = StudentID
GROUP BY C.NAME
You are missing the ON part for the join otherwise it would just be a CROSS JOIN.
Your first query should look like this if you want just a distinct list of student names:
SELECT DISTINCT C.NAME
FROM Course C
INNER JOIN Registration R ON C.CID = R.CourseID
INNER JOIN Student S ON R.StudentID = S.SID
WHERE Age < 20
Your second query shouldn't really have the C.Name in the select if you want to get just a count unless you want a count of how many students have that name.
SELECT count(*)
FROM Student S
INNER JOIN Registration R ON s.SID = R.StudentID
INNER JOIN Course C ON c.CID = R.CourseID
WHERE Age < 20
GROUP BY C.NAME
First join these tables, then group by Course's PK(CID), Add the HAVING condition to filter the course which has students younger than 20.
Then use Course table to join the result to get the course name and count of students in the course.
SELECT
T1.Name,
T2.StudentCount
FROM
Course T1
INNER JOIN (
SELECT
c.CID,
COUNT(s.SID) AS StudentCount
FROM
Course c
LEFT JOIN Registration r ON c.CID = r.CourseID
LEFT JOIN Student s ON s.SID = r.StudentID
GROUP BY c.CID
HAVING COUNT(IF(s.Age < 20, 1, NULL)) > 0
) T2 ON T1.CID = T2.CID
More correctly, you should move the conditions of the join, to the join statements themselves by including them in the on clause instead of the where. While the results may not change in this instance, if you were to start including outer joins you would encounter difficulties.
SELECT count(S.NAME)
,C.NAME
FROM Student S
INNER JOIN Registration R
ON s.SID = R.StudentID
INNER JOIN Course C
ON c.CID = R.CourseID
WHERE Age < 20
GROUP BY C.NAME
There's a fiddle here showing it in action: http://sqlfiddle.com/#!9/c3b8f/1
Your first query will also produce the results you want, but again, you should move the join predicates to the join itself. Also, you don't need to perform the grouping just to get distinct values, mysql has an expression for that called distinct. So rewritten, the first query would look like:
SELECT DISTINCT C.NAME
FROM Student S
INNER JOIN Registration R
ON s.SID = R.StudentID
INNER JOIN Course C
ON c.CID = R.CourseID
WHERE Age < 20.
Again, the results are the same as what you have already but it is easier to 'read' and will put you in good stead when you move on to other queries. As it stands you have mixed implicit and explicit join syntax.
This fiddle demonstrates both queries: http://sqlfiddle.com/#!9/c3b8f/4
edit
I may have misinterpreted your original question - if you want the total number of students enrolled in a course with at least one student under 19, you can use a query like this:
select name, count(*)
from course c
inner join registration r
on c.cid = r.courseid
where exists (
select 1
from course cc
inner join registration r
on cc.cid = r.courseid
inner join student s
on s.sid = r.studentid
where cc.cid = c.cid
group by cc.cid
having min(s.age) < 20
)
group by name;
Again with the updated fiddle here: http://sqlfiddle.com/#!9/c3b8f/17
I have three tables, libraryitems, copies and loans.
A libraryitem hasMany copies, and a copy hasMany loans.
I'm trying to get the latest loan entry for a copy only; The query below returns all loans for a given copy.
SELECT
libraryitems.title,
copies.id,
copies.qruuid,
loans.id AS loanid,
loans.status,
loans.byname,
loans.byemail,
loans.createdAt
FROM copies
INNER JOIN libraryitems ON copies.libraryitemid = libraryitems.id AND libraryitems.deletedAt IS NULL
LEFT OUTER JOIN loans ON copies.id = loans.copyid
WHERE copies.libraryitemid = 1
ORDER BY copies.id ASC, loans.createdAt DESC
I know there needs to be a sub select of some description in here, but struggling to get the correct syntax. How do I only return the latest, i.e MAX(loans.createdAt) row for each distinct copy? Just using group by copies.id returns the earliest, rather than latest entry.
Image example below:
in the subquery , getting maximum created time for a loan i.e. latest entry and joining back with loans to get other details.
SELECT
T.title,
T.id,
T.qruuid,
loans.id AS loanid,
loans.status,
loans.byname,
loans.byemail,
loans.createdAt
FROM
(
SELECT C.id, C.qruuid, L.title, MAX(LN.createdAt) as maxCreatedTime
FROM Copies C
INNER JOIN libraryitems L ON C.libraryitemid = L.id
AND L.deletedAt IS NULL
LEFT OUTER JOIN loans LN ON C.id = LN.copyid
GROUP BY C.id, C.qruuid, L.title) T
JOIN loans ON T.id = loans.copyid
AND T.maxCreatedTime = loans.createdAt
A self left join on loans table will give you latest loan of a copy, you may join the query to the other tables to fetch the desired output.
select * from loans A
left outer join loans B
on A.copyid = B.copyid and A.createdAt < B.createdAt
where B.createdAt is null;
This is your query with one simple modification -- table aliases to make it clearer.
SELECT li.title, c.id, c.qruuid,
l.id AS loanid, l.status, l.byname, l.byemail, l.createdAt
FROM copies c INNER JOIN
libraryitems li
ON c.libraryitemid = li.id AND
li.deletedAt IS NULL LEFT JOIN
loans l
ON c.id = l.copyid
WHERE c.libraryitemid = 1
ORDER BY c.id ASC, l.createdAt DESC ;
With this as a beginning let's think about what you need. You want the load with the latest createdAt date for each c.id. You can get this information with a subquery:
select l.copyid, max(createdAt)
from loans
group by l.copyId
Now, you just need to join this information back in:
SELECT li.title, c.id, c.qruuid,
l.id AS loanid, l.status, l.byname, l.byemail, l.createdAt
FROM copies c INNER JOIN
libraryitems li
ON c.libraryitemid = li.id AND
li.deletedAt IS NULL LEFT JOIN
loans l
ON c.id = l.copyid LEFT JOIN
(SELECT l.copyid, max(l.createdAt) as maxca
FROM loans
GROUP BY l.copyid
) lmax
ON l.copyId = lmax.copyId and l.createdAt = lmax.maxca
WHERE c.libraryitemid = 1
ORDER BY c.id ASC, l.createdAt DESC ;
This should give you the most recent record. And, the use of left join should keep all copies, even those that have never been leant.
I have a mysql query as stated below, it returns exactly the results I want for one row, but doesn't return any other rows where I expect there to be 8 in my test data (there are 8 unique test ids). I was inspired by this answer but obviously messed up my implementation, does anyone see where I'm going wrong?
SELECT
c.first_name,
c.last_name,
n.test_name,
e.doc_name,
e.email,
e.lab_id,
a.test_id,
a.date_req,
a.date_approved,
a.accepts_terms,
a.res_value,
a.reason,
a.test_type,
a.date_collected,
a.date_received,
k.kind_name,
sum(case when metabolite_name = "Creatinine" then t.res_val end) as Creatinine,
sum(case when metabolite_name = "Glucose" then t.res_val end) as Glucose,
sum(case when metabolite_name = "pH" then t.res_val end) as pH
FROM test_requisitions AS a
INNER JOIN personal_info AS c ON (a.user_id = c.user_id)
INNER JOIN test_types AS d ON (a.test_type = d.test_type)
INNER JOIN kinds AS k ON (k.id = d.kind_id)
INNER JOIN test_names AS n ON (d.name_id = n.id)
INNER JOIN docs AS e ON (a.doc_id = e.id)
INNER JOIN test_metabolites AS t ON (t.test_id = a.test_id)
RIGHT JOIN metabolites AS m ON (m.id = t.metabolite_id)
GROUP BY a.test_id
ORDER BY (a.date_approved IS NOT NULL),(a.res_value IS NOT NULL), a.date_req, c.last_name ASC;
Most of your joins are inner joins. The last is a right outer join. As written, the query keeps all the metabolites, but not necessarily all the tests.
I would suggest that you change them all to left outer joins, because you want to keep all the rows in the first table:
FROM test_requisitions AS a
LEFT JOIN personal_info AS c ON (a.user_id = c.user_id)
LEFT JOIN test_types AS d ON (a.test_type = d.test_type)
LEFT JOIN kinds AS k ON (k.id = d.kind_id)
LEFT JOIN test_names AS n ON (d.name_id = n.id)
LEFT JOIN docs AS e ON (a.doc_id = e.id)
LEFT JOIN test_metabolites AS t ON (t.test_id = a.test_id)
LEFT JOIN metabolites AS m ON (m.id = t.metabolite_id)
I would also suggest that your aliases be related to the table, so tr for test_requisition, pi for personal_info, and so on.