Need help understanding range between in SQL window functions - sql

Question

I am trying understand how range clause is working in below case (oracle database)
SELECT
EMPID,NAME,
HIRE_DATE_1,
SALARY,
count(1) over(order by HIRE_DATE_1 range between 1 preceding and 1 preceding) as PREV_MIN_SA
FROM (
SELECT
EMPID,
NAME,
(EXTRACT(year from HIRE_DATE)*10000)+(EXTRACT(MONTH FROM HIRE_DATE) * 100) + (extract(DAY from HIRE_DATE)) as HIRE_DATE_1,SALARY
FROM EMPLOYEE A order by HIRE_DATE,SALARY
) A
ORDER BY HIRE_DATE_1
Result Set :
EMPID NAME HIRE_DATE_1 SALARY PREV_MIN_SA
100 Ravi 20180101 5000 0
101 Kumar 20180101 7000 0
102 Satish 20180101 13000 0
103 Naresh 20180102 7500 3
105 Lalith 20180104 17300 0
104 Suresh 20180104 40000 0
106 Latha 20180201 16000 0
The inner query is just converting date into numeric YYYYMMDD format.
My intention is to get the count of people who joined immediately prior to the date of the employee in each record. I can take the count of rows with same HIRE_DATE and use LAG function but somehow not understand how the sql is returning this result set.
Also, once I am done with the counts I would like to get the MIN(SALARY) of the employees who joined immediately prior to the employee in current row and find the difference in salaries so wondering if somehow I can define the window to only have all records with immediately prior HIRE_DATE.
Thanks

Answer 1

This should get the preceding hire date...
SELECT
EMPID,NAME, HIRE_DATE, SALARY,
MAX(HIRE_DATE) OVER (ORDER BY HIRE_DATE
RANGE BETWEEN UNBOUNDED PRECEDING
AND INTERVAL '1 DAY' PRECEDING
)
AS PREV_HIRE_DATE
FROM
EMPLOYEE
Then I think you need to join back on to the employee table to find the number of employees and their min salary?
SELECT
*
FROM
(
SELECT
EMPID,NAME, HIRE_DATE, SALARY,
MAX(HIRE_DATE) OVER (ORDER BY HIRE_DATE
RANGE BETWEEN UNBOUNDED PRECEDING
AND INTERVAL '1 DAY' PRECEDING
)
AS PREV_HIRE_DATE
FROM
EMPLOYEE
)
EMPS
LEFT JOIN
(
SELECT
HIRE_DATE,
COUNT(*) AS COUNT_EMPS,
MIN(SALARY) AS MIN_SALARY
FROM
EMPLOYEE
GROUP BY
HIRE_DATE
)
PREV_EMPS
ON PREV_EMPS.HIRE_DATE = EMPS.PREV_HIRE_DATE
EDIT:
Maybe try something like this? (I have to run, good luck!)
WITH
ranked AS
(
SELECT
*,
DENSE_RANK() OVER (ORDER BY HIRE_DATE) AS HIRE_SEQ_ID
FROM
EMPLOYEE
)
SELECT
*,
MIN(SALARY) OVER (ORDER BY HIRE_SEQ_ID
RANGE BETWEEN 1 PRECEDING AND 1 PRECEDING
)
AS PREV_MIN_SALARY,
COUNT(*) OVER (ORDER BY HIRE_SEQ_ID
RANGE BETWEEN 1 PRECEDING AND 1 PRECEDING
)
AS COUNT_PREV_EMPS
FROM
ranked

Answer 2

This does what you're after, I believe (I've left it as an exercise for you to find the difference between the max and min salaries!):
WITH employee AS (SELECT 100 empid, 'Ravi' NAME, to_date('01/01/2018', 'dd/mm/yyyy') hire_date, 5000 salary FROM dual UNION ALL
SELECT 101 empid, 'Kumar' NAME, to_date('01/01/2018', 'dd/mm/yyyy') hire_date, 7000 salary FROM dual UNION ALL
SELECT 102 empid, 'Satish' NAME, to_date('01/01/2018', 'dd/mm/yyyy') hire_date, 13000 salary FROM dual UNION ALL
SELECT 103 empid, 'Naresh' NAME, to_date('02/01/2018', 'dd/mm/yyyy') hire_date, 7500 salary FROM dual UNION ALL
SELECT 104 empid, 'Lalith' NAME, to_date('04/01/2018', 'dd/mm/yyyy') hire_date, 17300 salary FROM dual UNION ALL
SELECT 105 empid, 'Suresh' NAME, to_date('04/01/2018', 'dd/mm/yyyy') hire_date, 40000 salary FROM dual UNION ALL
SELECT 106 empid, 'Latha' NAME, to_date('01/02/2018', 'dd/mm/yyyy') hire_date, 16000 salary FROM dual)
SELECT empid,
NAME,
hire_date,
salary,
COUNT(*) OVER (ORDER BY hire_date RANGE BETWEEN 1 PRECEDING AND 1 PRECEDING) prev_day_hire_count,
MIN(salary) OVER (ORDER BY hire_date RANGE BETWEEN 1 PRECEDING AND 1 PRECEDING) prev_day_min_sal,
MAX(salary) OVER (ORDER BY hire_date RANGE BETWEEN 1 PRECEDING AND 1 PRECEDING) prev_day_max_sal
FROM employee;
EMPID NAME HIRE_DATE SALARY PREV_DAY_HIRE_COUNT PREV_DAY_MIN_SAL PREV_DAY_MAX_SAL
---------- ------ ----------- ---------- ------------------- ---------------- ----------------
100 Ravi 01/01/2018 5000 0
101 Kumar 01/01/2018 7000 0
102 Satish 01/01/2018 13000 0
103 Naresh 02/01/2018 7500 3 5000 13000
104 Lalith 04/01/2018 17300 0
105 Suresh 04/01/2018 40000 0
106 Latha 01/02/2018 16000 0