Wrong count result - sql-server

Question

I have 2 tables in sql server:
Employee (Job Title, Hire Date)
Person (FirstName, LastName)
And I need to return the E.JobTitle, E.HireDate,P.FirstName ,P.LastName along with the how many employees have the same job title.
so I used this query:
SELECT E.JobTitle,
E.HireDate,
P.FirstName,
P.LastName,
COUNT(E.JobTitle)
FROM AdventureWorks2019.HumanResources.Employee E
JOIN AdventureWorks2019.Person.Person P ON E.BusinessEntityID = P.BusinessEntityID
GROUP BY E.JobTitle,
E.HireDate,
P.FirstName,
P.LastName;
the problem is that the query returns 1 per the count, while I'd expect to get per each row the count of the num employees with that job title.
my question is how can I get the correct count?

Answer 1

As mentioned by #Larnu in the comments, your issue is that you're grouping by LastName also, so you are going to get a count of 1 per LastName.
You need a windowed count with OVER, not an aggregated one with GROUP BY
No extra joins or grouping needed.
SELECT E.JobTitle,
E.HireDate,
P.FirstName,
P.LastName,
COUNT(*) OVER (PARTITION BY E.JobTitle)
FROM AdventureWorks2019.HumanResources.Employee E
JOIN AdventureWorks2019.Person.Person P ON E.BusinessEntityID = P.BusinessEntityID;

Answer 2

You should count the number of employee for each job title first in a subquery or cte.
SELECT
JobTitle,
COUNT(*) AS Count
FROM HumanResources.Employee
GROUP BY JobTitle
Then you can join the subquery or the cte with your original query.
WITH cte
AS
(
SELECT
JobTitle,
COUNT(*) AS Count
FROM HumanResources.Employee
GROUP BY JobTitle
)
SELECT
E.JobTitle,
E.HireDate,
P.FirstName,
P.LastName,
cte.Count
FROM
HumanResources.Employee E
INNER JOIN Person.Person P ON P.BusinessEntityID = E.BusinessEntityID
INNER JOIN cte on cte.JobTitle = E.JobTitle
ORDER BY
E.JobTitle,
P.LastName,
P.FirstName
;