I have database of doctors and hospital joined by hospitaldoctor table.
I have to List town, amount of hospitals in each town, but only hospitals which have more than 5 doctors.
SELECT hospital.town, count(town)
FROM hospital
WHERE hospital.id = (
SELECT count(hospital_id)
FROM hospital_doctor GROUP BY hospital_id
HAVING count(hospital_id)>5 )
GROUP BY town
this is my query but MySQL returns me that subquery returns more than 1 row.
HOSPITAL
HOSPITAL DOCTOR
How i should write this query?
You can do what you want with basically the same structure:
Select h.town, count(*)
from hospital h
where h.id in (select hd.hospital_id
from hospital_doctor hd
group by hd.hospital_id
having count(*) > 5
)
group by h.town ;
Note the following:
You want to use in not =, because the subquery could return more than one row.
The subquery should be returning the hospital id not the count.
Use table aliases and qualified column names whenever a table refers to more than one table.
SELECT h.town, count(h.town)
FROM
(
SELECT hospital_id
FROM hospital_doctor GROUP BY hospital_id
HAVING count(doctor_id)>5
) s1
left outer join hospital h on (s1.hospital_id=h.id)
GROUP BY h.town
Select hospital.town, count(town)
from hospital
where
hospital.id in (
select hospital_id
from hospital_doctor
group by hospital_id
having count(hospital_id)>5
)
group by town
Related
"employee" Table
emp_id
empName
1
ABC
2
xyx
"client" Table:
id
emp_id
clientName
1
1
a
2
1
b
3
1
c
4
2
d
"collection" Table
id
emp_id
Amount
1
2
1000
2
1
2000
3
1
1000
4
1
1200
I want to aggregate values from the three tables input tables here reported as samples. For each employee I need to find
the total collection amount for that employee (as a sum)
the clients that are involved with the corresponding employee (as a comma-separated value)
Here follows my current query.
MyQuery:
SELECT emp_id,
empName,
GROUP_CONCAT(client.clientName ORDER BY client.id SEPARATOR '') AS clientName,
SUM(collection.Amount)
FROM employee
LEFT JOIN client
ON clent.emp_id = employee.emp_id
LEFT JOIN collection
ON collection.emp_id = employee.emp_id
GROUP BY employee.emp_id;
The problem of this query is that I'm getting wrong values of sums and clients when an employee is associated to multiple of them.
Current Output:
emp_id
empName
clientName
TotalCollection
1
ABC
a,b,c,c,b,a,a,b,c
8400
2
xyz
d,d
1000
Expected Output:
emp_id
empName
clientName
TotalCollection
1
ABC
a , b , c
4200
2
xyz
d
1000
How can I solve this problem?
There are some typos in your query:
the separator inside the GROUP_CONCAT function should be a comma instead of a space, given your current output, though comma is default value, so you can really omit that clause.
each alias in your select requires the table where it comes from, as long as those field names are used in more than one tables among the ones you're joining on
your GROUP BY clause should at least contain every field that is not aggregated inside the SELECT clause in order to have a potentially correct output.
The overall conceptual problem in your query is that the join combines every row of the "employee" table with every row of the "client" table (resulting in multiple rows and higher sum of amounts during the aggregation). One way for getting out of the rabbit hole is a first aggregation on the "client" table (to have one row for each "emp_id" value), then join back with the other tables.
SELECT emp.emp_id,
emp.empName,
cl.clientName,
SUM(coll.Amount)
FROM employee emp
LEFT JOIN (SELECT emp_id,
GROUP_CONCAT(client.clientName
ORDER BY client.id) AS clientName
FROM client
GROUP BY emp_id) cl
ON cl.emp_id = emp.emp_id
LEFT JOIN (SELECT emp_id, Amount FROM collection) coll
ON coll.emp_id = emp.emp_id
GROUP BY emp.emp_id,
emp.empName,
cl.clientName
Check the demo here.
Regardless of my comment, here is a query for your desired output:
SELECT
a.emp_id,
a.empName,
a.clientName,
SUM(col.Amount) AS totalCollection
FROM (SELECT e.emp_id,
e.`empName`,
GROUP_CONCAT(DISTINCT c.clientName ORDER BY c.id ) AS clientName
FROM employee e
LEFT JOIN `client` c
ON c.emp_id = e.emp_id
GROUP BY e.`emp_id`) a
LEFT JOIN collection col
ON col.emp_id = a.emp_id
GROUP BY col.emp_id;
When having multiple joins, you should be careful about the relations and the number of results(rows) that your query generates. You might as well have multiple records in output than your desired ones.
Hope this helps
SELECT emp_id,
empName,
GROUP_CONCAT(client.clientName ORDER BY client.id SEPARATOR '') AS clientName,
C .Amount
FROM employee
LEFT JOIN client
ON clent.emp_id = employee.emp_id
LEFT JOIN (select collection.emp_id , sum(collection.Amount ) as Amount from collection group by collection.emp_id) C
ON C.emp_id = employee.emp_id
GROUP BY employee.emp_id;
it works for me now
I have the following table called Stores:
Name | Category | Industry
ABC appliances retail
XYZ banking finance
NZE clothing retail
JKI tutoring education
I would like to output all the Names that are the only one in their Industry (e.g. XYZ and JKI are the only Names in their Industry).
I have the following query:
select s.Name, s.Industry, a.Number
from Stores s
inner join (
select Industry, count(*) as Number
from Stores group by Industry
) a
on s.Industry = a.Industry;
I get an output table which has an attribute called Number which gives the total number of times each Industry appears in the table Stores. How can I select all the tuples which have the value of 1 in the Number column after using the inner join?
use where condition
select s.Name, s.Industry, a.Number
from Stores s
inner join (
select Industry, count(*) as Number
from Stores group by Industry
) a
on s.Industry = a.Industry where a.Number=1
use corelated subquery
select s.* from stores s
where exists ( select 1 from Stores s1 where s.Industry=s1.Industry
having count(*)=1)
You can use EXISTS :
SELECT s.*
FROM Stores s
WHERE EXISTS (SELECT 1 FROM Stores s1 WHERE s1.Industry = s.Industry AND s1.Name <> s.Name);
I would just use aggregation:
select industry, max(name) as name
from stores
group by industry
having count(*) = 1;
If there is only one name, then max(name) is the one.
If names can be repeated in the table, then:
having min(name) = max(name)
Lets say I have this tables:
country:
country_id,
country_name;
currency:
currency_id,
currency_name;
country_currency:
country_id,
currency_id;
I would like to select and show all countries having two or more currencies. How should my query look like?
Join all the tables with the common columns, then group the result by country_id, and count the number of rows (or currency) per group as shown below.
SELECT A.COUNTRY_ID, COUNT(*) NUMBER_OF_CURRENCY
FROM COUNTRY A
INNER JOIN COUNTRY_CURRENCY B ON A.COUNTRY_ID = B.COUNTRY_ID
INNER JOIN CURRENCY C ON B.CURRENCY_ID=C.CURRENCY_ID
GROUP BY A.COUNTRY_ID
HAVING NUMBER_OF_CURRENCY > 1 ;
A better query would be:
SELECT COUNTRY_NAME
FROM COUNTRY
WHERE COUNTRY_ID IN (
SELECT COUNTRY_ID
FROM COUNTRY_CURRENCY
GROUP BY COUNTRY_ID
HAVING COUNT(*) > 1
);
I have two tables as such:
student department
id department_id department_id department_name
5 5 5 Computer Science
1 4 4 Architecture
3 2 1 Mathematics
4 5 3 Chemistry
2 4 2 Physics
I wrote a query as follow and got the following results.
SELECT DEPARTMENTS.DEPT_NAME AS D, STUDENTS.DEPT_ID AS D_ID
FROM STUDENTS
INNER JOIN DEPARTMENTS
ON STUDENTS.DEPT_ID=DEPARTMENTS.DEPT_ID ;
Computer Science 5
Computer Science 5
Physics 2
Architecture 4
Architecture 4
It's fine till here but I want something like
Computer Science 2
Architecture 2
Physics 1
Chemistry 0
Mathematics 0
i.e department name , num_of students where num_of students are in decending order.
What can I add to the query?
I would use COUNT(*) and subquery it for the ORDER BY
SELECT * FROM (
SELECT DEPARTMENTS.DEPT_NAME, COUNT(*) AS num_ofstudents
FROM STUDENTS
LEFT JOIN DEPARTMENTS
ON STUDENTS.DEPT_ID=DEPARTMENTS.DEPT_ID
GROUP BY Departments.Dept_name
) AS a ORDER BY num_ofstudents
edit- Thanks AaronDietz for pointing this out!
You should replace the INNER JOIN with a LEFT JOIN so that the query includes the records from [Departments] that do not have any students. Also, I did not need to include the subquery.
SELECT DEPARTMENTS.DEPT_NAME, COUNT(*) AS num_ofstudents
FROM STUDENTS
LEFT JOIN DEPARTMENTS
ON STUDENTS.DEPT_ID=DEPARTMENTS.DEPT_ID
GROUP BY Departments.Dept_name
ORDER BY num_ofstudents
You can try grouping the departments and the id, then count.
SELECT DEPARTMENTS.DEPT_NAME AS D, COUNT(*) as NID
FROM STUDENTS
INNER JOIN DEPARTMENTS
ON STUDENTS.DEPT_ID=DEPARTMENTS.DEPT_ID
GROUP BY DEPARTMENTS.DEPT_NAME
ORDER BY NID DESC
I think the simplest approach is to select the departments and get the count in a subquery:
select
department_id,
department_name,
(select count(*) from student s where s.department_id = d.department_id) as student_count
from department d
order by 3 desc;
This works well, because you just want one value from the students, namely the count. If you wanted more information then you'd move the subquery to the from clause. E.g.:
select
d.department_id,
d.department_name,
colalesce(s.students, 0) as student_count,
s.ids as student_ids
from department d
left join
(
select
department_id,
count(*) as students,
group_concat(id) as ids
from student
group by department_id
) s on s.department_id = d.department_id
order by 3 desc;
SELECT DEPARTMENTS.DEPT_NAME AS D, count(STUDENTS.DEPT_ID) AS D_ID
FROM STUDENTS
INNER JOIN DEPARTMENTS
ON STUDENTS.DEPT_ID=DEPARTMENTS.DEPT_ID
GROUP BY D
ORDER BY D_ID DESC;
Grouping by department name
Other queries are mostly right but COUNT should be on student id and query should start from department instead of student.
SELECT DEPARTMENTS.DEPT_NAME,
COUNT(id) AS num_ofstudents
FROM DEPARTMENT
LEFT JOIN students ON STUDENTS.DEPT_ID = DEPARTMENTS.DEPT_ID
GROUP BY DEPARTMENTS.DEPT_NAME
ORDER BY num_ofstudents
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