Row_number() is non diterministic.

Question

hi,
empid frist name sal DEPARTMENT_ID
123     Shanta     7000          50
122     Payam     8000          50
120     Matthew 8000          50
121     Adam     Fripp 8200 50
SELECT
Department_id, first_name, salary,
ROW_NUMBER() OVER (PARTITION BY department_id ORDER BY salary desc) RN_NO
FROM employees
ORDER BY department_id, salary
i read that row_number is non deterministin so i show that if it is non deterministic then also i will have
empid frist name sal DEPARTMENT_ID RN_NO
123     Shanta     7000          50 4
122     Payam     8000          50 3
120     Matthew 8000          50 2
121     Adam     Fripp 8200 50 1
or this
empid frist name sal DEPARTMENT_ID RN_NO
123     Shanta     7000          50 4
122     Payam     8000          50 2
120     Matthew 8000          50 3
121     Adam     Fripp 8200 50 1
that is empid 122 and 120 may get 2 or 3 but empid 121 will get 1 and 123 will get 4 RN_NO.
please correct me.
yours sincerely

Answer 1

Hi,
944768 wrote:
hi,
empid frist name sal DEPARTMENT_ID
123     Shanta     7000          50
122     Payam     8000          50
120     Matthew 8000          50
121     Adam     Fripp 8200 50
SELECT
Department_id, first_name, salary,
ROW_NUMBER() OVER (PARTITION BY department_id ORDER BY salary desc) RN_NO
FROM employees
ORDER BY department_id, salary
i read that row_number is non deterministin so i show that if it is non deterministic then also i will have
empid frist name sal DEPARTMENT_ID RN_NO
123     Shanta     7000          50 4
122     Payam     8000          50 3
120     Matthew 8000          50 2
121     Adam     Fripp 8200 50 1
You may have those results. There is no guarantee that you will ever get the results above; you might happen to always get the results below. Then again, you might happen to get the results above every time. You just can't rely on getting one set or the other.
or this
empid frist name sal DEPARTMENT_ID RN_NO
123     Shanta     7000          50 4
122     Payam     8000          50 2
120     Matthew 8000          50 3
121     Adam     Fripp 8200 50 1
that is empid 122 and 120 may get 2 or 3 but empid 121 will get 1 and 123 will get 4 RN_NO.
please correct me.There's nothing to correct; you seem to have it right.
<tt> ROW_NUMBER () OVER (PARTITION BY x ORDER BY y) </tt> will be non-deterministic among rows that have exactly the same values of both x and y.
In your example, there is only 1 row with depatment_id=121 and sal=8200, so that row will always get the same ROW_NUMBER.
In your example, there are more than 1 rows with depatement_id=50 and sal=8000, so you can't be sure which of those will be assigned the number 2, and which will get 3.