I'm new to Oracle.
Now, I want to show number of employees working in each department,
and number of employees in each department must be less than 2.
But I only show department_id and department_name
I don't know how to show count.
SELECT d.DEPARTMENT_ID, d.DEPARTMENT_NAME
FROM DEPARTMENTS d
WHERE 2 > (SELECT COUNT(e.EMPLOYEE_ID)
FROM EMPLOYEES e
WHERE d.DEPARTMENT_ID = e.DEPARTMENT_ID);
My output:
DEPARTMENT_ID | DEPARTMENT_NAME
... | ...
Correct output:
DEPARTMENT_ID | DEPARTMENT_NAME | COUNT(EMPLOYYE_ID) |
... | ... | ... |
try this (added correction for handling cases of departments without employees)
SELECT d.DEPARTMENT_ID, d.DEPARTMENT_NAME, NVL(e2.cnt,0) count
FROM DEPARTMENTS d
LEFT JOIN (select e.department_id, count(*) cnt from employees e group by e.department_id) e2
ON d.department_id=e2.department_id
where e2.cnt <2
Or, more compact
SELECT d.DEPARTMENT_ID, d.DEPARTMENT_NAME, count(e2.employee_id)
FROM DEPARTMENTS d
LEFT JOIN employees e ON d.department_id=e.department_id
GROUP BY d.DEPARTMENT_ID, d.DEPARTMENT_NAME
HAVING COUNT(*) <2
Related
I need to select city, max salary in the city and employee name whose salary is max from Oracle HR Schema.
I try to do below code, but city name repeats:
select l.city, e.last_name, e.salary from locations l
inner join departments d on l.location_id = d.location_id
inner join employees e on d.department_id = e.department_id
and e.salary = (select max(salary) from employees where department_id = d.department_id)
group by l.city, e.last_name, e.salary
order by e.salary;
What is wrong with my code?
I've attached result, which I need.Correct SQL result
You can use the DENSE_RANK analytic function (which will return all employees with the maximum salary per city):
SELECT city,
last_name,
salary
FROM (
SELECT l.city,
e.last_name,
e.salary,
DENSE_RANK() OVER (
PARTITION BY l.location_id
ORDER BY e.salary DESC
) AS rnk
FROM locations l
INNER JOIN departments d
ON l.location_id = d.location_id
INNER JOIN employees e
ON d.department_id = e.department_id
)
WHERE rnk = 1;
or aggregation with KEEP (which will only return one employee with the maximum salary and the maximum last name per location):
SELECT MAX(l.city) AS city,
MAX(e.last_name) KEEP ( DENSE_RANK LAST ORDER BY e.salary ) AS last_name,
MAX(e.salary) AS salary
FROM locations l
INNER JOIN departments d
ON l.location_id = d.location_id
INNER JOIN employees e
ON d.department_id = e.department_id
GROUP BY
l.location_id
What is wrong with my code?
You are correlating on department_id = d.department_id and not on the location (or city name; however, don't aggregate on the city name as there could be two different locations with the same name).
I have 2 data tables, Employees and Departments. I want to show the department numbers, department names, the number of employees in each department, the average salary of each department, the employee names, their salaries, and jobs IDs of the employees. Here's what I wrote for my code:
select d.department_id, d.department_name, e.count(*) Employees,
avg(e.salary) Avg_salary, e.last_name, e.salary, e.job_id
from departments d join employees e
on d.department_id = e.department_id
group by d.department_id, d.department_name, e.last_name, e.salary, e.job_id
order by d.department_id;
However, the error "Missing Function" appears when I run the code. How do I fix it?
try this:
SELECT d.department_id,
d.department_name,
Count(*) Employees,
Avg(e.salary) Avg_salary,
e.last_name,
e.salary,
e.job_id
FROM departments d
JOIN employees e
ON d.department_id = e.department_id
GROUP BY d.department_id,
d.department_name,
e.last_name,
e.salary,
e.job_id
ORDER BY d.department_id;
e.count(*) should just be count(*).
EDIT:
Is this what you need?
COUNT(*) OVER (PARTITION BY e.department_id) DeptCt
I want to convert Subquery into Join, following is the subquery
SELECT employee_id, last_name, salary
FROM employees
WHERE salary > (SELECT AVG(salary)
FROM employees);
I wrote following join, but I am getting "ORA-00934: group function is not allowed here" error
SELECT e.employee_id,
e.last_name,
e.salary
FROM employees e
INNER JOIN employees average
ON(e.salary>AVG(average.salary));
You can use this like
SELECT e.employee_id,
e.last_name,
e.salary
FROM employees e
INNER JOIN (select AVG(salary) salary from employees ) average
ON (e.salary > average.salary)
Group by e.employee_id;
My objective is simple, I have to create a temporary table with some random values from a employee table whenever the department is in some particular department (say 2). For the rest of departments I don't care the value, it can be NULL.
Currently I have the following :
create table test
as
select s.DEPTNAME,
cast (
(case when s.DEPTID in (2) then
(SELECT a.ENAME FROM
(SELECT b.ENAME, b.DEPTID FROM EMPLOYEE b
WHERE b.DEPTID IS NOT NULL
ORDER BY DBMS_RANDOM.VALUE) a
WHERE a.DEPTID = s.DEPTID AND ROWNUM = 1
)
END)
AS VARCHAR2(30)) "ENAME" from DEPARTMENT s;
But the main issue here is related to performance. For every department value in 2 we do a sort of EMPLOYEE table to get a single random ENAME.
Is there a better way to do this ? I know sample might work but I want to achieve more randomness.
First idea - join randomly numbered enames:
with
e as (select ename, deptid, row_number() over (order by dbms_random.value) rn
from employee where deptid = 2),
c as (select count(1) cnt from e),
d as (select deptname, deptid, round(dbms_random.value(1, c.cnt)) rn from department, c)
select d.deptname, e.ename from d left join e using (rn, deptid)
SQLFiddle demo
Second possible solution, which worked for me, is to create function returning random ename from table employee
and use it in your query, but it would be probably slower.
Edit - according to comment:
If, for some reason, the first part of your statement is "fixed", then you could use this syntax:
create table test as
select deptname, ename from (
with
e as (select ename, deptid, row_number() over (order by dbms_random.value) rn
from employee where deptid = 2),
c as (select count(1) cnt from e),
d as (select deptname, deptid, round(dbms_random.value(1, c.cnt)) rn
from department cross join c)
select d.deptname, e.ename from d left join e using (rn, deptid));
I want to do this excercise for Oracle 10g Express
"Write an SQL query to retrieve the department name, firstname,
lastname, salary of the employee who earns the maximum salary for that
department."
I tried this code but it is not working for me.
There are two tables named employees, departments
ERROR is: ORA-00979: not a GROUP BY expression
SELECT first_name, last_name, departments.department_name, salary
FROM employees, departments
where employees.department_id = departments.department_id
group by salary
Output must be like that.
You will want to use an aggregate function to get the result. In this case you will use max() to get the highest salary for each department.
There are several ways that this can be written.
You can use a subquery in a join:
select d.department_name,
e.first_name,
e.last_name,
e.salary
from employees e
inner join
(
select max(salary) MaxSalary, department_id
from employees
group by department_id
) e1
on e.department_id = e1.department_id
and e.salary = e1.maxsalary
inner join departments d
on e.department_id = d.department_id;
Since you are using Oracle, you can use windowing functions to get the result:
select department_name, first_name, last_name, salary
from
(
select d.department_name,
e.first_name,
e.last_name,
e.salary,
row_number() over(partition by d.department_id order by e.salary desc) rn
from employees e
inner join departments d
on e.department_id = d.department_id
) d
where rn = 1
Or you can even use a WHERE clause to filter the data:
select d.department_name,
e.first_name,
e.last_name,
e.salary
from employees e
inner join departments d
on e.department_id = d.department_id
where salary in (select max(salary)
from employees e1
where e.department_id = e1.department_id
group by department_id)
I understand the question that you are asking is in reference to using GROUP BY but I would take a closer look at the question.
"Write an SQL query to retrieve the department name, firstname, lastname, salary of the employee who earns the maximum salary for that department."
I think you would also benefit from looking at the Maximum function since you are looking for the employee with the Maximum salary.
You need an aggregate function to be able to use GROUP BY. Aggregate functions are functions that perform a task over several records. These are functions like SUM, AVG, and COUNT. When you have an aggregate function, you group by whatever is not in the function.
In your example, MAX would be your aggregate function and you can use your GROUP BY successfully.
Here is a link for Aggregate Functions