I have a question about two queries. Will these two queries give the same result? I am trying to find the average salary by department:
Select s1.department, avg(s1.salary)
From
(Select department, salary
From staff
Where salary > 100000) s1
Group by s1.department
vs
select department, avg(salary) as avg_salary
from staff
where salary > 100000
group by department
Yes, it gives the same amounts back.
the bottom query gets data from a sub select which gets its data from the table, whereas the top query gets it straight from the table itself.
There are no additional filters in there. So the result will be the same.
you can test it out however, don't take my word for it.
Related
I have an Employees table which looks like this:
employee_id employee_name employee_salary
1 Tom 35000
2 Sarah 50000
3 David 45000
4 Rosie 55000
5 Michael 45000
I need to return the employees salary that is higher than the average salary but the below command is having an error saying '1 misuse of aggregate function AVG()'.
SELECT employee_salary
FROM Employees
WHERE employee_salary > AVG(employee_salary);
The output that I'm expecting to get is:
employee_id employee_name employee_salary
2 Sarah 50000
4 Rosie 55000
Please advise, thank you!
I need to write the SQL query to return the number of employees for each department.
I assume you're looking for something like this:
SELECT department_id
,COUNT(employee_id) AS TotalEmployees
FROM Department
LEFT JOIN Employees
ON Employees.department_id = Department.department_id
GROUP BY department_id
Also, I need to return the employees salary that is higher than the average salary
The simplest way to return the salaries that are higher than average as a beginner sql programmer is probably something like this:
SELECT employee_salary
FROM Employees
WHERE employee_salary > (SELECT AVG(employee_salary)
FROM Employees)
As the others said, the other questions just require a bit of research. There are tonnes of resources out there to learn, but it takes time...
I need to write the SQL query to return the number of employees for each
department. However, my below command is not correct:
This is not what you ask for.
You get the join correct, but you ask for:
SELECT COUNT(Employees.employment_id)
The count how often different employment id's exist - which is 1 for an employee in one department, or X with X being the number of entries in the join. As the department_id entry is part of the employee table, this CAN NOT HAPPEN. TOTALLY not asking what you want.
I'm using the LEFT JOIN here because I am returning the result from the
Employees table is this right?
Depends - a normal join should work here. Left is only sensible if the other side can be empty - which I would assume is not possible (there are no rows with Employees.department_id being NULL).
You you want is a count (without anything in the brackets) and a group by department_id. And obviously the department id:
SELECT Department.department_id, count() FROM....
Furthermore, are there any tips to speed up SQL Server's performance?
Just pointing you to https://use-the-index-luke.com/ - indices are a cornerstone for any decent performance.
Ignoring your second question - one per question please.
Apologies for my simple problem, I am an absolute novice. I have the following code in separate queries
I am attempting to display 3 columns, the average male salary for a set job, average female salary for a set job and the JobID. Separately these queries work however I cannot work out how to combine them.
I have tried multiple solutions from this site for example trying to put multiple select statements inside
and also by using a 'union' solution however cannot get either to work.union This simply compiles them into a single column and sorts via salary not JobID.
SELECT Round(Avg(Salary)) AS AverageMaleSalary, JobID
FROM Employee WHERE Gender = "M"
GROUP BY JobID;
SELECT Round(Avg(Salary)) AS AverageFemaleSalary, JobID
FROM Employee WHERE Gender = "F"
GROUP BY JobID;
You could use conditional aggregation
SELECT JobId,ROUND(AVG(IIF(Gender='F', Salary, NULL))) AS AverageFemaleSalary
,ROUND(AVG(IIF(Gender='M', Salary, NULL))) AS AverageMaleSalary
FROM Employee
GROUP BY JobId;
I need to write a query where I need to first count the people working in a department, then calculate the average people working in a department and finally round it to only one decimal place. I tried so many different variations.
That's what I got so far although it's not the first one I tried but I always get the same error message. (ORA-00979 - not a group by expression)
SELECT department_id,
ROUND(AVG(c.cnumber),1)
FROM employees c
WHERE c.cnumber =
(SELECT COUNT(c.employee_id)
FROM employees c)
GROUP BY department_id;
I really don't know what do to at this point and would appreciate any help.
Employees Table:
Try this (Oracle syntax) example from your description:
with department_count as (
SELECT department_id, COUNT(c.employee_id) as employee_count
FROM employees c
group by department_id
)
SELECT department_id,
ROUND(AVG(c.employee_count),1)
FROM department_count c
GROUP BY department_id;
But this query not make sense. Count is integer, and count return one number for one department in this case AVG return the same value as count.
Maybe you have calculate number of employee and averange of salary on department?
I will explain the problem I am stuck on. I have a table named empl02 which contains Lastname, salary, and position for all the employees. I am asked to display last,name,salary, position for all employees making more money than the highest paid member of a certain 'position', we will call this position server. I cannot just do something simple like...
SQL> select Lastname,salary,position FROM empl02
2 WHERE
3 SAL > 125000;
Rather, it must be dynamic. I feel the logic is pretty simple I'm just not sure how to translate it into SQL. I am thinking something along the lines of
"SELECT Lastname,salary,position from empl02 where salary > MAX(SALARY) of position(server)" what is a way to translate this task to SQL?
You need to retrieve the "reference" salary as a sub-query:
select lastname, salary, position
from empl02
where salary > (select max(salary)
from empl02
where position = 'manager');
employee database
SELECT name, MIN(salary)
FROM employee
GROUP BY deptid;
Why I can't select "name" here?
And what is the suggested query for this question?
Why I can't select "name" here?
You can only use columns or expressions the the SELECT if they are present in the GROUP BY area, or part of a function that calculates an aggregation.
Think of grouping like buckets. When you say group by dept_id if there are 3 departments (even if they are mentioned 20 times; 20 employees in departments A,A,A,A,A,A,A,A,A,A,A,A,B,B,B,B,B,C,C,C) you get 3 buckets and there's a label on the outside of each bucket, one for each different value of dept_id (a bucket for A, a bucket for B and a bucket for C). Into those buckets, all the employees rows are thrown according to which department they're in: 12 rows in A, 5 rows in B, 3 rows in C. Then you say MIN(salary), the db searches each bucket looking for the minimum salary.
Why can't you say name? There simply isn't a bucket for it. Your buckets are labelled A, B and C for the departments. No bucket has a name written on it. While there are names inside the bucket, you can only ask for them in terms of a MIN, MAX, AVG, SUM, COUNT etc - it's the rule. "To get something out of a bucket you have to use some kind of function that calculates some statistic". Actually, in some DBs you can ask for a CSV string of all the names, but we'll ignore that because it's accessory to the main point: unless you use an aggregate function you can only ask for something written on the outside of a bucket
What information should the DB give you if you ask for name?
You could ask for MIN(name), but you'd only get one name. You could GROUP BY Name.. but then you'd have a lot more buckets, and your employees would be redistributed across the buckets. You would't be asking for the MIN salary per department bucket any more, you'd be asking for the min salary per name.. Not what you want
And what is the suggested query for this question?
Break it down:
"minimum salary in the department"
We're going to need a list of all departments and the minimum salary in the department
SELECT dept_id, MIN(salary) as min_sal_for_dept
FROM employee
GROUP BY dept_id
"Find all the emps .. who earn minimum salary in their department"
Now we know that the depatment ID and min salary is for that department, we can join it back to the employee data on the department id and the salary
SELECT *
FROM
(
SELECT dept_id, MIN(salary) as sal
FROM employee
GROUP BY dept_id
) dep_min_sals
INNER JOIN
employee e
ON
e.dept_id = dep_min_sals.dept_id AND e.salary = dep_min_sals.sal
"display result in salary ascending order"
ORDER BY sal
The key thing to realize is that you have to group up (lose) detail in order to get the minimum salary per department, so if you want the detail back you have to join the grouped up data back to the detail. You cannot both lose the detail to calculate the minimum AND also keep the detail to have the employee name
A database-independent solution is to filter with a subquery:
select e.*
from emp e
where e.salary = (select min(e1.salary) from emp e1 where e1.deptid = e.deptid)
order by e.salary