Having hard time understanding SQL Query - sql

Question

I ran across this query and having hard time understanding what it does
SELECT DISTINCT
EMPLOYEE.EMPLOYEE_ID,
EMPLOYEE.LAST_NAME,
EMPLOYEE.FIRST_NAME,
COUNT(*)
FROM EMPLOYEE
JOIN ENTRY ON EMPLOYEE.EMPLOYEE_ID = ENTRY.EMPLOYEE_ID
JOIN TICKET ON ENTRY.TICKET_ID = TICKET.TICKET_ID
WHERE ENTRY.ACTIVITY_ID = 'ADVTS' AND EMPLOYEE.DEPARTMENT_ID ='SLS'
GROUP BY EMPLOYEE.EMPLOYEE_ID, EMPLOYEE.LAST_NAME,
EMPLOYEE.FIRST_NAME,ENTRY.ENTRY_ID
HAVING COUNT(ENTRY.ENTRY_ID) >=
(SELECT CAST(1.25 * COUNT(ENTRY.ACTIVITY_ID)/COUNT(DISTINCT EMPLOYEE.EMPLOYEE_ID) AS float)
FROM
EMPLOYEE
JOIN
ENTRY ON EMPLOYEE.EMPLOYEE_ID = ENTRY.EMPLOYEE_ID
WHERE
ENTRY.ACTIVITY_ID = 'ADVTS' AND EMPLOYEE.DEPARTMENT_ID = 'SLS')
As far as I understand it gives a list of EMPLOYEEs who done ADVTS ACTIVITY and from DEPARTMENT SLS which made ENTRYs at least as much as Average entries made in the DEPARTMENT SLS for ADVTS purposes
Thanks to anyone who take their time to help
Edit succesful result after comments:
SELECT
EMPLOYEE.EMPLOYEE_ID,
EMPLOYEE.LAST_NAME,
EMPLOYEE.FIRST_NAME
FROM EMPLOYEE
JOIN
ENTRY ON ENTRY.EMPLOYEE_ID = EMPLOYEE.EMPLOYEE_ID
GROUP
BY EMPLOYEE.EMPLOYEE_ID, EMPLOYEE.LAST_NAME,
EMPLOYEE.FIRST_NAME
HAVING
COUNT(ENTRY.ENTRY_ID) >=
(SELECT
CAST(1.25 *
COUNT(ENTRY.ACTIVITY_ID)/COUNT(DISTINCT EMPLOYEE.EMPLOYEE_ID)AS float)
FROM
EMPLOYEE JOIN ENTRY ON EMPLOYEE.EMPLOYEE_ID = ENTRY.EMPLOYEE_ID
WHERE
ENTRY.ACTIVITY_ID = 'ADVTS' AND EMPLOYEE.DEPARTMENT_ID = 'SLS')
OUTPUT:
EMPLOYEE_ID| LAST_NAME| FIRST_NAME
7 | Salesman | Efficient

Answer 1

Assuming that TICKET_ID is unique in Ticket and is never NULL in ENTRY, then you can get rid of that JOIN.
Then I assume the purpose of the query is to return employees whose count is more than 1.25 the overall average. That requires a few more (reasonable) assumptions, but this is more simply written as:
SELECT e.*
FROM (SELECT EM.EMPLOYEE_ID, EM.LAST_NAME, EM.FIRST_NAME, COUNT(*) AS CNT,
SUM(COUNT(*)) OVER () * 1.0 / COUNT(*) OVER () as AVG_CNT
FROM EMPLOYEE EM JOIN
ENTRY EM
ON EM.EMPLOYEE_ID = EN.EMPLOYEE_ID
WHERE EN.ACTIVITY_ID = 'ADVTS' AND EM.DEPARTMENT_ID = 'SLS'
GROUP BY EM.EMPLOYEE_ID, EM.LAST_NAME, EM.FIRST_NAME
) e
WHERE cnt >= 1.25 * avg_cnt