I have 2 tasks:
1. FIRST TASK
Show first_name, last_name (from employees), job_title, employee_id (from jobs) start_date, end_date (from job_history)
My idea:
SELECT s.employee_id
, first_name
, last_name
, job_title
, employee_id
, start_date
, end_date
FROM employees
INNER JOIN jobs hp
on s.employee_id = hp.employee_id
INNER JOIN job_history
on hp.jobs = h.jobs
I know it doesn't work. I'm receiving: "HP"."EMPLOYEE_ID": invalid identifier
What does it mean "on s.employee_id = hp.employee_id". Maybe I should write sthg else instead of this.
2. SECOND TASK
Show department_name (from departments), average and max salary for each department (those data are from employees) and how many employees are working in those departments (from employees). Choose only departments with more than 1 person. The result round to 2 decimal places.
I have the pieces, but i don't know to connect it
My idea:
SELECT department_name,average(salary),max(salary),count(employees_id)
FROM employees
INNER JOIN departments
on employees_id = departments_id
HAVING count(department) > 1
SELECT ROUND(average(salary),2) from employees
I modified your queries a bit by improving table aliasing. Hopefully, if the right columns are present in the tables as you say, it should work:
SELECT s.employee_id, s.first_name, s.last_name,
hp.job_title, hp.employee_id,
h.start_date, h.end_date
FROM employees s
INNER JOIN jobs hp
on s.employee_id = hp.employee_id
INNER JOIN job_history h
on hp.jobs = h.jobs;
When we say on s.employee_id = hp.employee_id it means that if, for example, there is an employee_id = 1234 present in both the tables employees and jobs, then SQL will bring all the columns from both the tables in the same line that corresponds to employee_id = 1234. You can now pick different columns in the SELECT clause as if they are in the same/single table(which was not the case before joining). This is the main logic behind SQL joins.
As to your 2nd task, try the below query. I made some modifications in aggregation by introducing COUNT(DISTINCT s.employees_id). If the same employees_id is present twice for some reason, you still want to count that as one person.
SELECT d.department_name, avg(s.salary), max(s.salary), count(distinct s.employees_id)
FROM employees s
INNER JOIN departments d
on e.employees_id = d.departments_id
GROUP BY d.department_name
HAVING COUNT(DISTINCT s.employees_id) > 1;
Let me know if there is still any issue. Hopefully, this works.
Related
I have a table of hospitals details, department details linked to it, types of workers (the staff) in different tables, and their salary information.
I want to extract the following for each hospital: the average and the sum of the salaries, the number of nurses, the number of research doctors and the number of beds in all the departments of a specific hospital.
I built this view of all the workers salary information:
CREATE VIEW workers AS
SELECT hospcod, docsal as sal, 'treatdoc' as typework
FROM doc NATURAL JOIN treatdoc NATURAL JOIN dept
UNION
SELECT hospcod, nursal, 'nurse'
FROM nurse NATURAL JOIN dept
UNION
SELECT hospcod, docsal, 'rsrchdoc'
FROM doc NATURAL JOIN rsrchdoc NATURAL JOIN lab;
the departments and the labs have the hospital code column to correlate a worker information to a specific hospital.
so I have one sceme for all the staff with their rules workers(hospital_code, salary, type_of_worker)
here is the query I'm trying to build:
SELECT hospname, sum(workers.sal), avg(workers.sal), count(dept.numbed),
(SELECT count(typework) from workers where typework = 'nurse') nurse_num,
(SELECT count(typework) from workers where typework = 'rsrchdoc') rsrchdoc_num
FROM hosp NATURAL JOIN dept NATURAL JOIN workers
GROUP BY hospname;
I want to count for each hospital, the number of nurses and the number of research doctors
but it should be correlated somehow to the different hospitals (in the above it gives me the same number of nurses / rsrchdocs for each hospital) , there should be columns that is grouped by hospnames and should get all the tuples like the salary info (avg, sum), as I got properly, but the workers information should be grouped HAVING typework = 'nurse' for the nurse_num, and for the column rsrchdoc_numit should be HAVING typework = 'rsrchdoc_num'
does someone have an idea how can I combine thouse columns in one query?
thank you!
There is an error in your query, I will try to explain.
When you do:
(SELECT count(typework) from workers where typework = 'nurse') nurse_num,
You are getting a constant, that is not affected by the "group by" you are doing after.
What you have to do is a JOIN (like you did in the view) and link the nurse and the rsrchdoc to an specific hospital.
I will give an example is pseudo code
SELECT hosp_name, sum(nurse.salary) , avg(nurse.salary)
FROM hosp
JOIN nurse ON nurse.hosp_name = hosp.hosp_name
GROUP BY hosp.hosp_name
This query will give you 1 row for each nurse in each hospital (assuming that a nurse may work in more than one hospital).
Then you have to do the same thing also for doctors, in a different operation.
SELECT hosp_name, sum(doctors.salary) , avg(doctors.salary)
FROM hosp
JOIN doctors ON doctors.hosp_name = hosp.hosp_name
GROUP BY hosp.hosp_name
And finally you will have to join both ( you may perform the sum first to make it more readable.
SELECT hosp_name, sum_sal_doc, avg_sal_doc, sum_nur_doc, avg_nur_doc
FROM hosp
LEFT JOIN ( SELECT doctors.hosp_name, sum(doctors.salary) as sum_sal_doc, avg(doctors.salary) as avg_sal_doc
FROM doctors
GROUP BY doctors.hosp_name
) t1 ON t1.hosp_name = hosp.hosp_name
LEFT JOIN ( SELECT nurses.hosp_name, sum(nurses.salary) as sum_nur_doc, avg(nurses.salary) as avg_nur_doc
FROM nurses
GROUP BY nurses.hosp_name
) t2 ON t2.hosp_name = hosp.hosp_name
There must be 1 to many relationship between hosp --> dept and hosp --> workers so if you join these 3 tables then you will definitely find the duplicates for dept and workers so you must have to create sub-query for one of the dept or workers to fetch single grouped record group by hospital as follows:
SELECT h.hospname,
sum(w.sal) total_all_worker_sal,
avg(w.sal) avg_all_workers_sal,
d.numbed,
count(case when w.typework = 'nurse' then 1 end) nurse_num,
count(case when w.typework = 'rsrchdoc' then 1 end) rsrchdoc_num
FROM hosp h
JOIN (select hospital_code , sum(numbed) numbed
-- used SUM as numbed must be number of bed in department
-- COUNT will give you only number of department if you use count(d.numbed)
from dept
group by hospital_code) d ON h.hospital_code = d.hospital_code
JOIN workers w ON h.hospital_code = d.hospital_code
GROUP BY h.hospital_code , h.hospname, d.numbed;
-- used h.hospital_code to separate the records if two hospitals have same name
1
select *
from employees
where salary > (select max(salary) from employees where department_id=50)
2
select *
from employees e left join
employees d
on e.DEPARTMENT_ID =d.DEPARTMENT_ID
where d.salary > (select max(salary) from employees where department_id=50)
why the second query is giving multiple record
i want achieve the same result as of 1st query using join.....
Thanks in Advance......
Rocky, the first select is correct. Why do you want to do any join? Without further information the objective of the second select is not clear (nonsense).
I can't see the point about joining against the same table by DEPARTMENT_ID. Anyway, the problem about duplicates is because you are joining the same two tables by a key is not pk, basically you are multiplyng each employee for all the employees of the same department. This version eliminate duplicates but still has no improvement from the first one.
select *
from employees e left join
employees d
on e.employee_ID = d.employee_ID
where d.salary > (select max(salary) from employees where department_id=50)
You are probably looking for an anti join. This is a pattern mainly used in a young DBMS where IN and EXISTS clauses are slow compared to joins, because the developers focused on joins only.
You are looking for all employees whose salaries are greater than all salaries in department 50. With other words: WHERE NOT EXISTS a salary greater or equal in department 50.
Your query can hence be written as:
select *
from employees e
where not exists
(
select null
from employees e50
where e50.department_id = 50
and e50.salary >= e.salary
);
As an anti join (an outer join where you dismiss all matches):
select *
from employees e
left join employees e50 on e50.department_id = 50 and e50.salary >= e.salary
where e50.salary is null;
This is the schema
\,
I try using inners but the results were trash
SELECT
employees.last_name AS last_name,
COUNT(employees.job_id) AS EMPLOYEES_Subordinates,
COUNT(employees.manager_id) AS Manager_Numbers
FROM
employees left
JOIN departments ON departments.manager_id = employees.manager_id
GROUP BY
employees.last_name
ORDER BY
EMPLOYEES_Subordinates desc;
( i really don't know how to show you the tables from hr)
If any 1 has the HR in Oracle Database and have time to help me , I gladly appreciate .
not quite sure but try something like this:
SELECT
e.LAST_NAME
,(SELECT COUNT(ee.EMPLOYEE_ID) FROM EMPLOYEES ee WHERE ee.MANAGER_ID = e.EMPLOYEE_ID) AS 'NUMBER OF WORKERS'
FROM EMPLOYEES e
WHERE MANAGER_ID IS NULL
Edit: Sorry! I am using Microsoft SQL Server.
For clarification, you can have a department named "x" with a list of jobs, a department named "y" with a different list of jobs, etc.
I also need to use >= ALL instead of TOP 1 or MAX because I need it to return more than one value if necessary (if job1 has 20 employees, job2 has 20 employees and they are both the biggest values, they should both return).
In my query I'm trying to find the most common jobTitle and the number of employees that work under this jobTitle, which is under the department 'Research and Development'. The query I've written consists of joins to be able to return the necessary data.
The problem I am having is with the WHERE statement. The HAVING COUNT(JobTitle) >= ALL is finding the biggest number of employees that work under a job, however the problem is that my WHERE statement is saying the Department must be 'Research and Development', but the job with the most amount of employees comes from a different department, and thus the output produces only the column names and nothing else.
I want to redo the query so that it returns the job with the largest amount of employees that comes from the Research and Development department.
I know this is probably pretty simple, I'm a noob :3 Thanks a lot for the help!
SELECT JobTitle, COUNT(JobTitle) AS JobTitleCount, Department
FROM HumanResources.Employee AS EMP JOIN
HumanResources.EmployeeDepartmentHistory AS HIST
ON EMP.BusinessEntityID = HIST.BusinessEntityID JOIN
HumanResources.Department AS DEPT
ON HIST.DepartmentID = DEPT.DepartmentID
WHERE Department = 'Research and Development'
GROUP BY JobTitle, Department
HAVING COUNT(JobTitle) >= ALL (
SELECT COUNT(JobTitle) FROM HumanResources.Employee
GROUP BY JobTitle
)
If you only want one row, then a typical method is:
SELECT JobTitle, COUNT(*) AS JobTitleCount
FROM HumanResources.Employee AS EMP JOIN
HumanResources.EmployeeDepartmentHistory AS HIST
ON EMP.BusinessEntityID = HIST.BusinessEntityID JOIN
HumanResources.Department AS DEPT
ON HIST.DepartmentID = DEPT.DepartmentID
WHERE Department = 'Research and Development'
GROUP BY JobTitle
ORDER BY COUNT(*) DESC
FETCH FIRST 1 ROW ONLY;
Although FETCH FIRST 1 ROW ONLY is the ANSI standard, some databases spell it LIMIT or even SELECT TOP (1).
Note that I removed DEPARTMENT both from the SELECT and the GROUP BY. It seems redundant.
And, if I had to guess, your query is going to overstate results because of the history table. If this is the case, ask another question, with sample data and desired results.
EDIT:
In SQL Server, I would recommend using window functions. To get the one top job title:
SELECT JobTitle, JobTitleCount
FROM (SELECT JobTitle, COUNT(*) AS JobTitleCount,
ROW_NUMBER() OVER (ORDER BY COUNT(*) DESC) as seqnum
FROM HumanResources.Employee AS EMP JOIN
HumanResources.EmployeeDepartmentHistory AS HIST
ON EMP.BusinessEntityID = HIST.BusinessEntityID JOIN
HumanResources.Department AS DEPT
ON HIST.DepartmentID = DEPT.DepartmentID
WHERE Department = 'Research and Development'
GROUP BY JobTitle
) j
WHERE seqnum = 1;
To get all such titles, when there are duplicates, use RANK() or DENSE_RANK() instead of ROW_NUMBER().
with employee_counts as (
select
hist.DepartmentID, emp.JobTitle, count(*) as cnt,
case when dept.Department = 'Research and Development' then 1 else 0 end as is_rd,
from HumanResources.Employee as emp
inner join HumanResources.EmployeeDepartmentHistory as hist
on hist.BusinessEntityID = emp.BusinessEntityID
inner join HumanResources.Department as dept
on dept.DepartmentID = hist.DepartmentID
group by
hist.DepartmentID, emp.JobTitle
)
select * from employee_counts
where is_rd = 1 and cnt = (
select max(cnt) from employee_counts
/* where is_rd = 1 */ -- ??
);
I have the database schema like this
Flights(flno,from,to,distance,departs,arrives,price)
Aircraft(aid,aname,cruisingRange)
Certified(employee,aircraft)
Employees(eid,ename,salary)
Where Flno is primary key and Each route corresponds to a "flno".
So I have this question to answer for the Schema
For each pilot, list their employee ID, name, and the number of routes
he can pilot.
I have this SQL, is this correct? ( I can test, as I dont have data for the database).
select eid, ename, count(flno)
from employees, flights
groupby flno
This is a simple questioin, but as everyone is mentioning you don't have any link between employee and flights. The relationships stop at certified.
You obviously have or will create some relationship. I have written a query that will give you the count taking into account that you will have a many to many relationship between employee and flights. Meaning an employee can have many flights and a single flight can be made by many employees.
Flights(flno,from,to,distance,departs,arrives,price)
Aircraft(aid,aname,cruisingRange)
Certified(employee,aircraft)
Employees(eid,ename,salary)
select
e.eid employee_id,
e.ename employee_name,
count(*)
from
employees e
inner join certified c on
c.employee = e.eid
inner join aircraft a on
a.aid = c.aircraft
inner join aircraft_flights af on -- new table that you would need to create
af.aircraft = a.aid and
inner join flights f on
f.flno = af.flno -- not I made up a relationship here which needs to exist in some for or another
group by
e.eid,
e.ename
I hope this at least shows you how to write a count statement correctly, but you should probably brush up on your understanding of joins.
Hope that helps.
EDIT
Without the relationships and working in your comments you could get the count as below.
select
e.eid employee_id,
e.ename employee_name,
count(*)
from
employees e
inner join certified c on
c.employee = e.eid
inner join aircraft a on
a.aid = c.aircraft
inner join flights f on
f.distance <= a.cruisingRange
group by
e.eid,
e.ename