I'm trying to make a query that looks at a single table to see if a student is in a team called CMHT and in a medic team - if they are I don't want to see the result.
I only want see the record if they're only in CMHT or medic, not both.
Would the right direction be using sub query to filter it out? I've done a search on NOT IN but how could you get to see check if its in more then 2 teams are not?
Student Team ref
1 CMHT 1
1 Medic 2
2 Medic 3 this would be in the result
3 CMHT 5 this would be in the result
So far I've done the following code would I need use a sub query or do a self join and filter it that way?
SELECT Table1.Student, Table1.Team, Table1.refnumber
FROM Table1
WHERE (((Table1.Team) In ('Medics','CMHT'))
This is Mark Byers's answer with a HAVING clause instead of a subquery:
SELECT Student, Team, ref
FROM Table1
GROUP BY Student
HAVING COUNT(Student) = 1
SELECT *
FROM students
WHERE NOT EXISTS
(
SELECT NULL
FROM students si
WHERE si.student = s.student
AND si.team = 'CMHT'
)
OR NOT EXISTS
(
SELECT NULL
FROM students si
WHERE si.student = s.student
AND si.team = 'Medic'
)
SELECT a.*
FROM Table1 a
INNER JOIN
( SELECT Student, COUNT(*) FROM Table1
GROUP BY Student
HAVING COUNT(*) = 1)b
ON (a.Student = b.Student)
how could you get to see check if its in 2 or more teams?
You can count the number of teams per student and then filter only those you want to see:
SELECT student FROM
(
SELECT student, COUNT(*) AS cnt
FROM Table1
GROUP BY student
) T1
WHERE cnt = 1
You can do it with outer join
select COALESCE(t1.Student, t2.Student) as Student,
COALESCE(t1.Team, t2.Team) as Team,
COALESCE(t1.ref, t2.ref) as ref
from
(select * from Student where Team = 'CMHT') t1
outer join
(select * from Student where Team = 'Medic') t2
on t1.Student = t2.Student
where
t1.Student is null or
t2.Student is null;
Related
I have these 3 tables and I am trying to count, how many "hints" and "quizzes" are there for specific town id.
db_town
id
town
1
New York
db_hint
id
town_id
hint
1
1
test
db_quiz
id
town_id
quiz
1
1
quiz 1
2
1
quiz 2
I am using this statement, but it does not work :(
SELECT count(q.id),count(h.id) FROM `db_town` t LEFT JOIN `db_quiz` q ON t.id = q.town_id LEFT JOIN `db_hint` h ON t.id = h.town_id WHERE t.id = 1 GROUP BY t.id
and it produces this result:
count(q.id)
count(h.id)
2
2
Do I need to use two statements? Or is it possible to query it in a single SQL statement? I am using MariaDB.
You can use union all and aggregation:
select town_id, sum(is_hint), sum(is_quiz)
from ((select town_id, 1 as is_hint, 0 as is_quiz
from hints
) union all
(select town_id, 0, 1
from quizzes
)
) t
group by town_id;
Alternatively, you can use correlated subqueries:
select t.*,
(select count(*) from hints h where h.town_id = t.id),
(select count(*) from quizzes q where q.town_id = t.id)
from towns t;
Two things to look out for:
JOINs are likely to multiply rows and throw off the counts.
Getting 0 values if a town has no hints or quizzes.
You can use COUNT (DISTINCT) if both the hint id and the quiz id are unique.
SELECT
count(distinct q.id),count(distinct h.id)
FROM `db_town` t
LEFT JOIN `db_quiz` q ON t.id = q.town_id
LEFT JOIN `db_hint` h ON t.id = h.town_id
WHERE t.id = 1 GROUP BY t.id
I'm trying to write sql query which return me subject_id(result table) where primary_skill(student table) is unique.
Result table has column (student_id, subject_id, mark)
My query:
SELECT r.subject_id
FROM result r
JOIN student s ON r.student_id = s.student_id
WHERE s.primary_skill IN (SELECT DISTINCT primary_skill
FROM student)
GROUP BY 1;
I have this result:
subject_id
1
2
3
4
5
6
7
8
9
10
1001
But I should return only id 1001, because only this subject has unique student primary_skill, in other ids primary skill are repeated.
What am I doing wrong? How it improve?
Please try following:
select result.subject_id from student
join result on student.id =result.student_id where
student.primary_skill in
(select primary_skill from student group by primary_skill having COUNT(*)=1)
If I understand this right, you want results for students only having one skill. You can use GROUP BY and a HAVING clause checking for the count of skill being equal to one for this.
SELECT r.subject_id
FROM result r
INNER JOIN (SELECT s.student_id
FROM student s
GROUP BY s.student_id
HAVING count(DISTINCT s.primary_skill) = 1) x
ON x.student_id = r.student_id;
I have two tables, student and school.
student
stid | stname | schid | status
school
schid | schname
Status can be many things for temporary students, but NULL for permanent students.
How do I list names of schools which has no temporary students?
Using Conditional Aggregate you can count the number of permanent student in each school.
If total count of a school is same as the conditional count of a school then the school does not have any temporary students.
Using JOIN
SELECT sc.schid,
sc.schname
FROM student s
JOIN school sc
ON s.schid = sc.schid
GROUP BY sc.schid,
sc.schname
HAVING( CASE WHEN status IS NULL THEN 1 END ) = Count(*)
Another way using EXISTS
SELECT sc.schid,
sc.schname
FROM school sc
WHERE EXISTS (SELECT 1
FROM student s
WHERE s.schid = sc.schid
HAVING( CASE WHEN status IS NULL THEN 1 END ) = Count(*))
You can use not exists to only select schools that do not have temporary students:
select * from school s
where not exists (
select 1 from student s2
where s2.schid = s.schid
and s2.status is not null
)
You can use a regular join.
SELECT DISTINCT c.schName
FROM Students s
INNER JOIN Schools c ON s.schid = c.schid
WHERE s.status IS NULL
I am using sql-server.I have a table looks like
StudentName Class score
Jim a1 80
Ann a1 83
Bill a2 90
I want to select student whose score is above the average score in his/her class. Here is my code:
Select a.StudentName
From Table a
inner Join Table b
On a.class=b.class
where a.score>(select avg(b.score) From b
group by class);
The inner join method looks odd to me.Is it correct please? Is there any better way to achieve that please?
You're close, but you can limit your sub-query and take out the JOIN:
Select a.StudentName
From Table a
where a.score > (
select avg(b.score) score
From Table b
where b.class = a.class);
How about:
;with ClassAverages as (
select Class, AVG(score) as AVGScore FROM Table GROUP BY Class
)
SELECT StudentName FROM Table student
INNER JOIN ClassAverages ON ClassAverages.Class=student.Class
WHERE student.score>ClassAverages.AVGScore
Say we have two entities:teacher and student.
each teacher has multiple student.
Now I want to:
query for at most 5 teachers,and for each teacher, no more than 10 of his student.
So far this can be done quite easily by:
select *,
(
select GROUP_CONCAT('<sid>',students.name,'</sid>') from students on
teachers.id=students.teacher limit 10
) as students
from teachers limit 5
But that's not the whole story yet.
AND
If anyone of the teachers has more than 10 students,should return true for that teacher,otherwise false
How to do this in SQL?
Pseudo SQL: one row of results for each of the 10 students for each of the 5 teachers
select t.teacher_id, s.student_id,
case when t2.count > 10 then 'true' else 'false' end
from
(select top 5 *
from teachers
order by teacher_id) t
join
(select top 10 *
from students s1 join teachers t1 on s1.teacher_id = t1.teacher_id
order by student_id) s
on t.teacher_id = s.teacher_id
join
(select teacher_id, count(*) as count
from teachers t join students s on t.teacher_id = s.teacher_id
group by teacher_id) t2
on t2.teacher_id = t.teacher_id
LINQ makes this super-easy
Use a subquery for every teacher selected.