So i have an employees table:
I'm trying to create a query that displays all the info of this employee but i'm a little stumped at the Employee_Reports_To bit. What i want to appear is the First_Name and Last_Name of the Employee_ID that's stored in this column (Eg Joe Bloggs ID 1, reports to employee Joanne Blog ID 50)
Would this need a join or just a simple select. The database is having issues with the link when i try..
SELECT employee.*, departments.Department_Name,
jobTitle.Job_Title,
(SELECT manager.First_Name, manager.Last_Name
FROM Employee manager
INNER JOIN employee AS employeeReportsTo
ON manager.Employee_Reports_To = manager.Employee_ID
) AS Reports_To
FROM Employee employee
LEFT JOIN Departments AS departments
ON departments.Departments_ID = employee.Departments_ID
LEFT JOIN Job_Title AS jobTitle
ON jobTitle.Job_Title_ID = employee.Job_Title_ID
ORDER BY `employee`.`Record_Active` DESC,
`employee`.`First_Name` ASC
Any assistance would be appreciated!
Try this solution:
SELECT emp.*,
manager.First_Name,
manager.Last_Name,
departments.Department_Name,
jobTitle.Job_Title
FROM Employee emp
INNER JOIN Employee manager
ON emp.Employee_Reports_To = manager.Employee_ID
LEFT JOIN Departments AS departments
ON departments.Departments_ID = emp.Departments_ID
LEFT JOIN Job_Title AS jobTitle
ON jobTitle.Job_Title_ID = emp.Job_Title_ID
ORDER BY emp.Record_Active DESC,
emp.First_Name ASC
It's always better to use Join instead of using Sub Query.
EDITED:
Since column Employee_Reports_To can be null so it's better to use LEFT JOIN instead of INNER JOIN. Like This:
SELECT emp.*,
manager.First_Name,
manager.Last_Name,
departments.Department_Name,
jobTitle.Job_Title
FROM Employee emp
LEFT JOIN Employee manager --Changed Join here
ON emp.Employee_Reports_To = manager.Employee_ID
LEFT JOIN Departments AS departments
ON departments.Departments_ID = emp.Departments_ID
LEFT JOIN Job_Title AS jobTitle
ON jobTitle.Job_Title_ID = emp.Job_Title_ID
ORDER BY emp.Record_Active DESC,
emp.First_Name ASC
Looking to your code you could use two time Employee (with alias e1 and e2) one for employee and one for the related manager
SELECT e1.*
, departments.Department_Name
, jobTitle.Job_Title
, e2.First_Name
,e2.Last_Name
FROM Employee e1
INNER JOIN Employee e2 ON e1.Employee_Reports_To = e2.Employee_ID
LEFT JOIN Departments AS departments
ON departments.Departments_ID = e1.Departments_ID
LEFT JOIN Job_Title AS jobTitle
ON jobTitle.Job_Title_ID = e1.Job_Title_ID
ORDER BY e1.`Record_Active` DESC,
e1.`First_Name` ASC
Related
I have 2 tables employees(id, first_name, last_name, salary, department_id_ and department(id, name) and I want to show number of employees in each department.
I have this question here:
SELECT department.name, COUNT(*) AS 'employees_number'
FROM department
LEFT JOIN employees
ON employees.department_id = department.id
GROUP BY department.id, department.name;
But for some reason, in departments where I have no people, it shows a number of employees as 1. Any idea why this is happening?
With an outer join you still get a result row when no match in the outer table is found. Only all employee column values are null then.
So rather than count the records, you want to count matched records, i.e. where an employee was found and its data is not null. So Count a column in the employee table (nulls are not counted, when counting a column or expression). E.g. use COUNT(e.department_id) or COUNT(e.id):
SELECT d.name, COUNT(e.id) AS employees_number
FROM department d
LEFT JOIN employees e ON e.department_id = d.id
GROUP BY d.id, d.name;
What I prefer though, is to aggregate/count before joining. The query looks a bit more complicated, but is less prone to errors on future query changes:
SELECT d.name, COALESCE(e.how_many, 0) AS employees_number
FROM department d
LEFT JOIN
(
SELECT department_id, COUNT(*) AS how_many
FROM employees
GROUP BY department_id
) e ON e.department_id = d.id;
As it's one aggregated column only you want, you can move the subquery to your SELECT clause and get thus a simpler query:
SELECT
d.name,
(
SELECT COUNT(*)
FROM employees e
WHERE e.department_id = d.id
) AS employees_number
FROM department d;
Using SUM instead of COUNT also can give you what you want:
SELECT
department.name,
SUM(CASE WHEN employees.id IS NOT NULL THEN 1 ELSE 0 END) AS 'employees_number'
FROM department
LEFT JOIN employees
ON employees.department_id = department.id
GROUP BY department.id, department.name;
SQL Fiddle:
http://sqlfiddle.com/#!9/8b8976/1
select department.name, count(employee.id) as co from
department left join employee on
department.id = employee.dept_id group by department.name
order by co desc, department.name asc
I need to make sql question which will show all departments with at least 2 people in it.
SELECT department.name
FROM department
INNER JOIN employee
ON department.id = employee.department_id
GROUP BY employee.id
HAVING COUNT(employee.id) >= 2;
It's not showing me anything with this query
I think you using GROUP BY on wrong column.
If you want to count employee in each department, then you need to GROUP BY department.id.
SELECT department.id, department.name, COUNT(employee.id) AS total_employee
FROM department
INNER JOIN employee
ON department.id = employee.department_id
GROUP BY department.id, department.name
HAVING COUNT(employee.id) >= 2;
Try this:
SELECT d.name
FROM department d
WHERE
(SELECT COUNT(*) FROM employee e
WHERE d.id = e.department_id) >= 2
In this way if you want to change your limit (instead of 2, another value) your query will work.
If you use INNER JOIN if you want, in the future all departments with no employees you can't use it.
I have two tables, for example the Employee and Project tables:
Employee (id, dept, joining_date)
Project (emp_id, project)
With Project having foreign key from Employee table.
I have to query on project and dept and return Employee in the order of their joining_date. Which query will work faster on big data set on the queries below?
select * from Employee where id in (select p.emp_id from Project p join Employee e on p.emp_id = e.id where p.project = 'project1' and e.dept = 'dept1') order by joining_date
select * from Employee where id in (select p.emp_id from Project p join Employee e on p.emp_id = e.id where p.project = 'project1' and e.dept = 'dept1') and dept = 'dept1' order by joining_date
Or is there any better and simpler way to do so?
The outer query using the IN() expression serves no purpose is entirely unnecessary. This will produce the output you need:
select e.*
from Project p
inner join Employee e on p.emp_id = e.id
where p.project = 'project1' and e.dept = 'dept1'
order by joining_date
SELECT
e.lname AS employee_name
, s.lname AS supervisor_name
, e.superssn AS supervisor_ssn
FROM employee e INNER JOIN employee s
WHERE e.superssn=s.ssn
I actually have two questions. The first one is, the above statement works just fine. However right now it will show bunch of employees with their supervisor. Not well organized. By the way there are three supervisors. Is there a way to show let's say supervisor A with employees A and supervisor B with employees B and so on?
The second problem is that I also tried to just count the number of employees for each supervisor rather than showing their name with COUNT(), I tried several different ones but non worked.
A few things
1) It is good practice to keep your join predicate with your join. So change:
FROM employee e INNER JOIN employee s WHERE e.superssn = s.ssn
To:
FROM employee e INNER JOIN employee s ON e.superssn = s.ssn
2) To keep them together by supervisor, just use an order by:
SELECT
e.lname AS employee_name
, s.lname AS supervisor_name
, e.superssn AS supervisor_ssn
FROM employee e INNER JOIN employee s ON e.superssn = s.ssn
ORDER BY s.lname
3) To do a count of employees for each supervisor use a group by and the COUNT aggregate function
SELECT
s.lname AS supervisor_name,
COUNT(*) AS employee_count
FROM employee e INNER JOIN employee s ON e.superssn = s.ssn
GROUP BY s.lname
ORDER BY s.lname
I have the folowing tables.
ORDER
OrderNumber
CustomerNumber
EmployeeNumber
OrderDate
CUSTOMER
CustomerNumber
Name
Address
EMPLOYEE
EmployeeNumber
Name
Address
ORDERDETAIL
OrderNumber
Qty
Description
Price
Let say ORDERDETAIL table has 10 records
I would like to write a query that will return 10 records from ORDERDETAIL table to include Employee name, employee address, customer name, customer address and and order Date.
I know that I could write a query and use INNER JOIN to get the info from ORDER table, but how do you create the rest of query to get the info from the CUSTOMER and EMPLOYEE tables.
SELECT *
FROM OrderDetail D
INNER JOIN Order O
ON D.OrderNumber = O.OrderNumber;
Just add some more joins...
SELECT *
FROM OrderDetail D
JOIN Order USING (OrderNumber)
JOIN Customer USING (CustomerNumber)
JOIN Employee USING (EmployeeNumber)
You might want to re-order the JOINs in order to have the smallest tables first, as this could provide you with some performance boost (depending on your server's version, the most recent will optimize the join for you and might actually execute the joins in the "probably best" way).
Also, in the MySQL dialect at least, JOIN implicitly expands to INNER JOIN, and writing
A JOIN B USING (COL)
is equivalent to writing
A JOIN B ON (A.COL = B.COL)
SELECT *
FROM OrderDetail D
INNER JOIN Order O ON D.OrderNumber = O.OrderNumber
INNER JOIN Eployee E on O.EployeeNumber = E.EployeeNumber
INNER JOIN Customer C on O.CustomerNumber = C.CustomerNumber
if you have foreign key reference between
ORDER.EmployeeNumber and EMPLOYEE.EmployeeNumber
ORDER.CustomerNumber and CUSTOMER.CustomerNumber
then try this
SELECT
E.name AS employeeName,
E.Address AS employeeAddress,
C.name AS customerName,
C.Address AS customerAddress.
O.OrderDate
FROM OrderDetail D
INNER JOIN Order O ON D.OrderNumber = O.OrderNumber
INNER JOIN EMPLOYEE E ON E.EmployeeNumber = 0.EmployeeNumber
INNER JOIN CUSTOMER C ON C.CustomerNumber= 0.CustomerNumber
LIMIT 0,10