https://towardsdatascience.com/mysql-how-to-write-a-query-that-returns-the-top-records-in-a-group-12865695f436#:~:text=MySQL%208.0%20introduces%20a%20rank,each%20row%20within%20each%20partition.
For each year and each month, rank records by decreasing order_amount.
year, month, amount, rank
2018, 11, 255.0, 1
2018, 11, 200.0, 2
2018, 11, 175.0, 3
...
2018, 12, 321.0, 1
2018, 12, 321.0, 1
2018, 12, 145.0, 2
...
MySQL 5.7 using variable assignment and IF(expr, true, false)
SELECT order_number, customer_number, customer_name, order_date,
YEAR(order_date) AS order_year,
MONTH(order_date) AS order_month,
order_amount,
@order_rank := IF(@current_month = MONTH(order_date),
@order_rank + 1, 1) AS order_rank,
@current_month := MONTH(order_date)
FROM orders
ORDER BY order_year, order_month, order_amount DESC
MySQL 8.0 using RANK() OVER(PARTITION BY ... ORDER BY ...)
SELECT order_number, customer_number, customer_name, order_date,
YEAR(order_date) AS order_year,
MONTH(order_date) AS order_month,
order_amount,
RANK() OVER (
PARTITION BY YEAR(order_date), MONTH(order_date)
ORDER BY YEAR(order_date), MONTH(order_date), order_amount DESC) order_value_rank
FROM orders;
SELECT RANK() OVER(ORDER BY cars_sold DESC) AS rank_sales,
first_name,
last_name,
cars_sold
FROM salespeople;
Window functions:
Table 12.26 Window Functions
| Name | Description |
|---|
CUME_DIST() | Cumulative distribution value |
DENSE_RANK() | Rank of current row within its partition, without gaps |
FIRST_VALUE() | Value of argument from first row of window frame |
LAG() | Value of argument from row lagging current row within partition |
LAST_VALUE() | Value of argument from last row of window frame |
LEAD() | Value of argument from row leading current row within partition |
NTH_VALUE() | Value of argument from N-th row of window frame |
NTILE() | Bucket number of current row within its partition. |
PERCENT_RANK() | Percentage rank value |
RANK() | Rank of current row within its partition, with gaps |
ROW_NUMBER() | Number of current row within its partition |
mysql> SELECT
val,
ROW_NUMBER() OVER w AS 'row_number',
CUME_DIST() OVER w AS 'cume_dist',
PERCENT_RANK() OVER w AS 'percent_rank'
FROM numbers
WINDOW w AS (ORDER BY val);
+------+------------+--------------------+--------------+
| val | row_number | cume_dist | percent_rank |
+------+------------+--------------------+--------------+
| 1 | 1 | 0.2222222222222222 | 0 |
| 1 | 2 | 0.2222222222222222 | 0 |
| 2 | 3 | 0.3333333333333333 | 0.25 |
| 3 | 4 | 0.6666666666666666 | 0.375 |
| 3 | 5 | 0.6666666666666666 | 0.375 |
| 3 | 6 | 0.6666666666666666 | 0.375 |
| 4 | 7 | 0.8888888888888888 | 0.75 |
| 4 | 8 | 0.8888888888888888 | 0.75 |
| 5 | 9 | 1 | 1 |
+------+------------+--------------------+--------------+
mysql> SELECT
time, subject, val,
SUM(val) OVER (PARTITION BY subject ORDER BY time
ROWS UNBOUNDED PRECEDING)
AS running_total,
AVG(val) OVER (PARTITION BY subject ORDER BY time
ROWS BETWEEN 1 PRECEDING AND 1 FOLLOWING)
AS running_average
FROM observations;
+----------+---------+------+---------------+-----------------+
| time | subject | val | running_total | running_average |
+----------+---------+------+---------------+-----------------+
| 07:00:00 | st113 | 10 | 10 | 9.5000 |
| 07:15:00 | st113 | 9 | 19 | 14.6667 |
| 07:30:00 | st113 | 25 | 44 | 18.0000 |
| 07:45:00 | st113 | 20 | 64 | 22.5000 |
| 07:00:00 | xh458 | 0 | 0 | 5.0000 |
| 07:15:00 | xh458 | 10 | 10 | 5.0000 |
| 07:30:00 | xh458 | 5 | 15 | 15.0000 |
| 07:45:00 | xh458 | 30 | 45 | 20.0000 |
| 08:00:00 | xh458 | 25 | 70 | 27.5000 |
+----------+---------+------+---------------+-----------------+
mysql> SELECT
time, subject, val,
FIRST_VALUE(val) OVER w AS 'first',
LAST_VALUE(val) OVER w AS 'last',
NTH_VALUE(val, 2) OVER w AS 'second',
NTH_VALUE(val, 4) OVER w AS 'fourth'
FROM observations
WINDOW w AS (PARTITION BY subject ORDER BY time
ROWS UNBOUNDED PRECEDING);
+----------+---------+------+-------+------+--------+--------+
| time | subject | val | first | last | second | fourth |
+----------+---------+------+-------+------+--------+--------+
| 07:00:00 | st113 | 10 | 10 | 10 | NULL | NULL |
| 07:15:00 | st113 | 9 | 10 | 9 | 9 | NULL |
| 07:30:00 | st113 | 25 | 10 | 25 | 9 | NULL |
| 07:45:00 | st113 | 20 | 10 | 20 | 9 | 20 |
| 07:00:00 | xh458 | 0 | 0 | 0 | NULL | NULL |
| 07:15:00 | xh458 | 10 | 0 | 10 | 10 | NULL |
| 07:30:00 | xh458 | 5 | 0 | 5 | 10 | NULL |
| 07:45:00 | xh458 | 30 | 0 | 30 | 10 | 30 |
| 08:00:00 | xh458 | 25 | 0 | 25 | 10 | 30 |
+----------+---------+------+-------+------+--------+--------+
https://en.wikipedia.org/wiki/Percentile_rank
