I'm trying to answer these questions but I'm not understanding the whole joining and functions part of MySQL. Can someone show me or explain these to me?
this is the link to the employee database we are using - https://github.com/datacharmer/test_db
I want to know how many employees with each title were born after 1965-01-01.
I want to know the average salary per title.
How much money was spent on salary for the marketing department between the years 1990 and 1992?
This is what I have so far for each one.
1.
select count(title) as "Number Of Employees", title from titles GROUP BY title LIMIT 20;
SELECT d.dept_name as "Department", avg(s.salary) as "Average Salary" from departments d
INNER JOIN dept_emp de on de.dept_no = d.dept_no
INNER JOIN salaries s on s.emp_no = de.emp_no
GROUP BY d.dept_name;
and this one seems like it's just those two put together so I completely don't understand it.
Join with the employee table so you can get the employee's date of birth.
SELECT t.title, COUNT(*) AS "Number of Employees"
FROM titles AS t
JOIN employees AS e ON e.emp_no = t.emp_no
WHERE e.birth_date > '1965-01-01'
GROUP BY t.title
You need to get the most recent salary for each employee and average that. And you have to join with the titles table so you can average by title.
SELECT t.title, AVG(salary)
FROM titles AS t
JOIN employees AS e ON e.emp_no = t.emp_no
JOIN (
-- subquery to get latest salary for each employee
-- See https://stackoverflow.com/questions/7745609/sql-select-only-rows-with-max-value-on-a-column?noredirect=1&lq=1
SELECT s.emp_no, s.salary
FROM salaries AS s
JOIN (
SELECT emp_no, MAX(from_date) AS max_date
FROM salaries
GROUP BY emp_no
) AS ms ON s.emp_no = ms.emp_no AND s.from_date = ms.from_date
) AS s ON e.emp_no = t.emp_no
GROUP BY t.title
I'm not even sure what the third question means. Does it mean the total salaries for all employees during those years? This seems incredibly complex for a beginner exercise, since you have to deal with different start/end dates for employees, and changing salaries during that period. I'm not even sure how to do that in a single query.
Related
I want to print name and salary amount of the employee which has highest salary, till now its okay but if there are multiple records than print all. There are two table given :-
EMPLOYEE TABLE :-
SALARY TABLE:-
my query is: -
SELECT E.NAME, S.AMOUNT
FROM `salary` S,
employee E
WHERE S.EMPLOYEE_ID = E.ID
and S.AMOUNT = (SELECT max(`AMOUNT`)
FROM `salary`)
is there any better way to find out the solution ?
It is "with ties" functionality what you're trying to achieve. Unfortunately mySQL doesn't support that (in the docs there is nothing to add to the "LIMIT" part of the query), so you have no other option rather than looking for max salary first and filter records afterwards.
So, your solution is fine for that case.
Alternatively, if you're on version 8 and newer, you may move the subquery to the with clause
with max_sal as (
select max(amount) ms from salary
)
SELECT E.NAME, S.AMOUNT
FROM salary S
JOIN employee E
ON S.EMPLOYEE_ID = E.ID
JOIN max_sal ms
ON S.AMOUNT = ms.ms
or search for it in the join directly
SELECT E.NAME, S.AMOUNT
FROM salary S
JOIN employee E
ON S.EMPLOYEE_ID = E.ID
JOIN (select max(amount) ms from salary) ms
ON S.AMOUNT = ms.ms
But I'm sure it won't get you any better performance
I like solving them with a join:
WITH M as (select max(amount) as amount from salary)
SELECT E.NAME, S.AMOUNT
FROM M JOIN SALARY USING(AMOUNT) JOIN Employee USING(Id)
but your solution is perfectly fine..
i want to find the age of employee with highest salary in the database.
i tried this query
SELECT DATEDIFF(SELECT DATE_FORMAT(SYSDATE(),'%Y-%m-%d'),
(SELECT birth_date FROM salaries as s, employees as e WHERE salary = (SELECT MAX(salary) FROM salaries) and s.emp_no = e.emp_no)/365.25);
but its not working.this picture contain database structure
Your original attempt seemed to have a number of minor problems, though the overall approach seems sound to me. Just take the DATEDIFF() between the birth date of the employee with the maximum salary and the current datetime.
SELECT DATEDIFF(SYSDATE(), e.birth_date) / 365.25
FROM salaries s
INNER JOIN employees e
ON s.emp_no = e.emp_no
WHERE s.salary = (SELECT MAX(salary) FROM salaries)
Changes I made include using an explicit inner join between your tables and also computing the date difference in a different way.
Note that this query would return stats for multiple employees should more than one employee tie for the maximum salary. In absence of further requirements, this seems like a reasonable thing to do.
So I'm trying to find the average time it takes for an employee to get a salary raise from the time of hiring.
I've tried a few things, but I'm not getting it right.
Here's what my database looks like:
https://dev.mysql.com/doc/employee/en/sakila-structure.html
This is what I've tried:
SELECT AVG(SUM(datediff(hire_date, min((SELECT from_date FROM salaries
WHERE from_date > hire_date AND
(SELECT salary FROM salaries
WHERE from_date = hire_date) <
(SELECT salary FROM salaries
WHERE from_date > hire_date))))))
FROM employees;
Any help would be greatly appreciated, logically this should be correct (maybe not), I'm probably just messing up with syntax some how..
Thanks!
This is not an easy query, but probably it is in the course for you to try to find it by yourself and, during that process, learn a lot of SQL.
In a real system development situation, if SQL gets too heavy or complex sometimes it is easier for the programmer to do more queries, use a stored procedure or solve it in the programming language.
But, as a help, I believe this would make the trick:
select avg(md) from (
select emp_no, min(days) as md from
(select s1.emp_no as emp_no,
s1.from_date as start,
datediff(s2.from_date,s1.from_date) as days
from employees e inner join salaries s1 on
e.emp_no=s1.emp_no
inner join salaries s2 on s1.emp_no=s2.emp_no
where
s2.from_date <> s1.from_date and
s1.from_date < s2.from_date and
s1.from_date = e.hire_date
) t ) tt group by emp_no
The idea is first make an expensive JOIN to find all differences of dates (from s2s2 - from of s1) but only when date_from is equal hire_date and the dates are not equal. (diff=0).
The second internal select gets the minimum value for each employee, this is for sure the first promotion.
The outer select makes the average.
This is how I would approach this to make things that you are trying to achieve explicit:
SELECT AVG(datediff(e.hire_date, second_salary.from_date))
FROM
employees e INNER JOIN
salaries first_salary ON e.emp_no = first_salary.emp_no AND
first_salary.from_date = e.hire_date INNER JOIN
salaries second_salary ON e.emp_no = second_salary.emp_no AND
second_salary.from_date > e.hire_date AND
second_salary.salary > frist_salary.salary AND
NOT EXISTS (SELECT * FROM salaries s
WHERE s.emp_no = e.emp_no AND
s.from_date > e.hire_date AND
s.from_date < second_salary.from_date AND
s.salary > first_salary.salary)
;
This type of analysis requires a lot of profiling and data quality validation though. I would not trust date conditions too much for this type of data.
I have mysql query that is.
select d.department_id,d.department_name,sum(e.salary) AS amount
from department d inner join employee e on d.department_id=e.department_id
group by d.department_id,d.department_name
I get grand total by using this query .
select d.department_id,d.department_name,sum(e.salary) AS amount
from department d inner join employee e on d.department_id=e.department_id
group by d.department_id,d.department_name WITH ROLLUP
But I want this grand total by sum amount column alias like this
select d.department_id,d.department_name,sum(e.salary) AS amount, sum(SELECT(amount)) AS grand_total
from department d inner join employee e on d.department_id=e.department_id
group by d.department_id,d.department_name
My database structure is .
And my tables are
But I want like this .
Please Help me any one.
If you want an additional column use a join or subquery:
select d.department_id, d.department_name, sum(e.salary) AS amount,
tot.salary
from department d inner join
employee e
on d.department_id = e.department_id inner join
(select sum(e.salary) as salary from employee) tot
group by d.department_id, d.department_name, tot.salary;
Note: this assumes that the total from the employee table is the total you want. This seems like a reasonable assumption, but it might not be accurate if some employees do not have departments or if some employees are in multiple departments. In that case, you just need to repeat the join to department in the subquery.
I have a problem with extracting data from db. My code looks like:
SELECT MAX(maximum)as Number FROM
(
SELECT department_name, COUNT(employees.employee_id) AS maximum
FROM departments, employees
WHERE departments.department_id=employees.department_id
GROUP BY department_name
)t
and the result is:
Number
1 46
and this is the number of maximum employees in one of the departments.
The problem is that i want to have additional column with the name of the department in wich there is 46 employees. I tried something like:
select department_name, count(employees.employee_id)
from departments, employees
where departments.department_id=employees.department_id
group by department_name
having count(employees.employee_id) =
( SELECT MAX(maxx)FROM
(SELECT department_name, COUNT(employees.employee_id) AS maxx
FROM departments, employees
WHERE departments.department_id=employees.department_id
GROUP BY department_name
);
but it doesn't work. Please help!
try this
SELECT t.department_name, MAX(t.maximum) as Number FROM (
SELECT
department_name,
COUNT(employees.employee_id) AS maximum
FROM departments, employees
WHERE departments.department_id=employees.department_id
GROUP BY department_name
) t
How about this just order your results by maximum in descending order with limit 1,also use modern join syntax query
SELECT d.department_name,
COUNT(e.employee_id) AS maximum
FROM departments d
LEFT JOIN employees e
ON (d.department_id=e.department_id)
GROUP BY d.department_name
ORDER BY maximum DESC
LIMIT 1
This will give you the department name who has the highest count of employees
You could also tack on an additional JOIN to the first query you posted as such:
SELECT TOP 1 d.department_name, MAX(maximum) as Number FROM
(
SELECT department_id AS department_id, COUNT(employees.employee_id) AS maximum
FROM departments, employees
WHERE departments.department_id=employees.department_id
GROUP BY department_id
)t
JOIN departments d ON d.department_id = t.department_id
GROUP BY d.department_name
ORDER BY Number DESC
I tried this with a similar data model in my domain and it works quite nicely.