SQL query within SQL query on sum - sql

Question

I have two tables, Employees and EmployeeVacations. I am trying to do a SQL query to get the sum of how much vacation time each employee has taken and their current balance as of today. Here is my current SQL query:
SELECT
e.PIN,
e.FirstName,
e.LastName,
e.Uniform,
e.AL_Cap,
ev.Value AS '10/1 Balance',
(SELECT
SUM(value)
FROM EmployeeVacations
WHERE CreationDate >= '2016-10-01'
AND Vacation_Type = 'Taken'
AND Vacation_Kind = 'AL'
AND EmployeeId = 13)
AS Taken
FROM employees e,
EmployeeVacations ev
WHERE e.Id = ev.EmployeeId
AND ev.IsHistory = 0
AND ev.Vacation_Type = 'Forward'
AND ev.Vacation_Kind = 'AL'
AND EmployeeId = 13
ORDER BY e.LastName, e.FirstName
This works if I pick a single employee. If I remove the "where EmployeeId = 13", I get a list of all the employees with the sum of everyone's total vacation in every row (like 1,300 hours). How do I break it down so it only shows the Taken for each employee specifically?

Answer 1

You need a corelated query, where the subquery uses a value from the "parent" query.
SELECT e.PIN ...
(select SUM(value) .... WHERE EmployeeID = e.id) as taken
^^^^^
Note that these can be very inefficient, since the inner query has to be executed once for every row of the parent query. IN a lot of cases, you may be better off re-writing as a conventional JOIN query with appropriate grouping.

Answer 2

Just guessing that you also might want the sum rather than the single forward records... Here is a query that aggregates EmployeeVacations per EmployeeId:
select
e.pin,
e.firstname,
e.lastname,
e.uniform,
e.al_cap,
ev.forward_sum as "10/1 balance",
ev.taken_sum as taken
from employee e
left join
(
select
employeeid,
sum(case when vacation_type = 'Forward'
and ishistory = 0 then value else 0 end) as forward_sum,
sum(case when vacation_type = 'Taken'
and creationdate >= '20161001' then value else 0 end) as taken_sum,
from employeevacations
where vacation_kind = 'AL'
group by employeeid
) ev on ev.employeeid = e.employeeid
order by e.lastname, e.firstname;
Please ...
use explicit joins instead of the pre-1992 comma-separated joins for readability and for being less prone to errors.
use double quotes for alias names; single quotes are for string literals.
use 'yyyymmdd' for dates; it is the supported date literal format in SQL Server.