Relational Data - Window Functions
UNBOUNDED FOLLOWING (END of the PARTITION)
### Functions
These functions can be used only as a window function.
- [`row_number()`](Relational_Data_-_Window_Functions_-_Row_Number) - Number the current row within its partition starting from 1.
- [`first_value(x)`](Relational_Data_-_Window_Functions_-_First_Value) - Return the first value evaluated within its ordered frame.
- [`last_value(x)`](Relational_Data_-_Window_Functions_-_Last_Value) - Return the last value evaluated within its ordered frame.
- [`nth_value(x, offset)`](Relational_Data_-_Window_Functions_-_Nth_Value) - Return the first non-NULL value evaluated against the nth row (offset) in its ordered frame.
- [`rank()`](Relational_Data_-_Window_Functions_-_Rank) - Rank the current row within its partition with gaps.
- [`dense_rank()`](Relational_Data_-_Window_Functions_-_Dense_Rank) - Rank the current row within its partition without gaps.
- [`lagInFrame(x)`](Relational_Data_-_Window_Functions_-_Lag_In_Frame) - Return a value evaluated at the row that is at a specified physical offset row before the current row within the ordered frame.
- [`leadInFrame(x)`](Relational_Data_-_Window_Functions_-_Lead_In_Frame) - Return a value evaluated at the row that is offset rows after the current row within the ordered frame.
## Examples
Let's have a look at some examples of how window functions can be used.
### Numbering rows
```sql
CREATE TABLE salaries
(
`team` String,
`player` String,
`salary` UInt32,
`position` String
)
Engine = Memory;
INSERT INTO salaries FORMAT Values
('Port Elizabeth Barbarians', 'Gary Chen', 195000, 'F'),
('New Coreystad Archdukes', 'Charles Juarez', 190000, 'F'),
('Port Elizabeth Barbarians', 'Michael Stanley', 150000, 'D'),
('New Coreystad Archdukes', 'Scott Harrison', 150000, 'D'),
('Port Elizabeth Barbarians', 'Robert George', 195000, 'M');
SELECT player, salary,
row_number() OVER (ORDER BY salary) AS row
FROM salaries;┌─player──────────┬─salary─┬─row─┐
│ Michael Stanley │ 150000 │ 1 │
│ Scott Harrison │ 150000 │ 2 │
│ Charles Juarez │ 190000 │ 3 │
│ Gary Chen │ 195000 │ 4 │
│ Robert George │ 195000 │ 5 │
└─────────────────┴────────┴─────┘SELECT player, salary,
row_number() OVER (ORDER BY salary) AS row,
rank() OVER (ORDER BY salary) AS rank,
dense_rank() OVER (ORDER BY salary) AS denseRank
FROM salaries;┌─player──────────┬─salary─┬─row─┬─rank─┬─denseRank─┐
│ Michael Stanley │ 150000 │ 1 │ 1 │ 1 │
│ Scott Harrison │ 150000 │ 2 │ 1 │ 1 │
│ Charles Juarez │ 190000 │ 3 │ 3 │ 2 │
│ Gary Chen │ 195000 │ 4 │ 4 │ 3 │
│ Robert George │ 195000 │ 5 │ 4 │ 3 │
└─────────────────┴────────┴─────┴──────┴───────────┘
Aggregation functions
Compare each player’s salary to the average for their team.
SELECT player, salary, team,
avg(salary) OVER (PARTITION BY team) AS teamAvg,
salary - teamAvg AS diff
FROM salaries;┌─player──────────┬─salary─┬─team──────────────────────┬─teamAvg─┬───diff─┐
│ Charles Juarez │ 190000 │ New Coreystad Archdukes │ 170000 │ 20000 │
│ Scott Harrison │ 150000 │ New Coreystad Archdukes │ 170000 │ -20000 │
│ Gary Chen │ 195000 │ Port Elizabeth Barbarians │ 180000 │ 15000 │
│ Michael Stanley │ 150000 │ Port Elizabeth Barbarians │ 180000 │ -30000 │
│ Robert George │ 195000 │ Port Elizabeth Barbarians │ 180000 │ 15000 │
└─────────────────┴────────┴───────────────────────────┴─────────┴────────┘Compare each player’s salary to the maximum for their team.
SELECT player, salary, team,
max(salary) OVER (PARTITION BY team) AS teamAvg,
salary - teamAvg AS diff
FROM salaries;┌─player──────────┬─salary─┬─team──────────────────────┬─teamAvg─┬───diff─┐
│ Charles Juarez │ 190000 │ New Coreystad Archdukes │ 190000 │ 0 │
│ Scott Harrison │ 150000 │ New Coreystad Archdukes │ 190000 │ -40000 │
│ Gary Chen │ 195000 │ Port Elizabeth Barbarians │ 195000 │ 0 │
│ Michael Stanley │ 150000 │ Port Elizabeth Barbarians │ 195000 │ -45000 │
│ Robert George │ 195000 │ Port Elizabeth Barbarians │ 195000 │ 0 │
└─────────────────┴────────┴───────────────────────────┴─────────┴────────┘
Partitioning by column
CREATE TABLE wf_partition
(
`part_key` UInt64,
`value` UInt64,
`order` UInt64
)
ENGINE = Memory;
INSERT INTO wf_partition FORMAT Values
(1,1,1), (1,2,2), (1,3,3), (2,0,0), (3,0,0);
SELECT
part_key,
value,
order,
groupArray(value) OVER (PARTITION BY part_key) AS frame_values
FROM wf_partition
ORDER BY
part_key ASC,
value ASC;
┌─part_key─┬─value─┬─order─┬─frame_values─┐
│ 1 │ 1 │ 1 │ [1,2,3] │ <┐
│ 1 │ 2 │ 2 │ [1,2,3] │ │ 1-st group
│ 1 │ 3 │ 3 │ [1,2,3] │ <┘
│ 2 │ 0 │ 0 │ [0] │ <- 2-nd group
│ 3 │ 0 │ 0 │ [0] │ <- 3-d group
└──────────┴───────┴───────┴──────────────┘
Frame bounding
CREATE TABLE wf_frame
(
`part_key` UInt64,
`value` UInt64,
`order` UInt64
)
ENGINE = Memory;
INSERT INTO wf_frame FORMAT Values
(1,1,1), (1,2,2), (1,3,3), (1,4,4), (1,5,5);-- Frame is bounded by bounds of a partition (BETWEEN UNBOUNDED PRECEDING AND UNBOUNDED FOLLOWING)
SELECT
part_key,
value,
order,
groupArray(value) OVER (
PARTITION BY part_key
ORDER BY order ASC
Rows BETWEEN UNBOUNDED PRECEDING AND UNBOUNDED FOLLOWING
) AS frame_values
FROM wf_frame
ORDER BY
part_key ASC,
value ASC;
┌─part_key─┬─value─┬─order─┬─frame_values─┐
│ 1 │ 1 │ 1 │ [1,2,3,4,5] │
│ 1 │ 2 │ 2 │ [1,2,3,4,5] │
│ 1 │ 3 │ 3 │ [1,2,3,4,5] │
│ 1 │ 4 │ 4 │ [1,2,3,4,5] │
│ 1 │ 5 │ 5 │ [1,2,3,4,5] │
└──────────┴───────┴───────┴──────────────┘-- short form - no bound expression, no order by
SELECT
part_key,
value,
order,
groupArray(value) OVER (PARTITION BY part_key) AS frame_values
FROM wf_frame
ORDER BY
part_key ASC,
value ASC;
┌─part_key─┬─value─┬─order─┬─frame_values─┐
│ 1 │ 1 │ 1 │ [1,2,3,4,5] │
│ 1 │ 2 │ 2 │ [1,2,3,4,5] │
│ 1 │ 3 │ 3 │ [1,2,3,4,5] │
│ 1 │ 4 │ 4 │ [1,2,3,4,5] │
│ 1 │ 5 │ 5 │ [1,2,3,4,5] │
└──────────┴───────┴───────┴──────────────┘-- frame is bounded by the beginning of a partition and the current row
SELECT
part_key,
value,
order,
groupArray(value) OVER (
PARTITION BY part_key
ORDER BY order ASC
Rows BETWEEN UNBOUNDED PRECEDING AND CURRENT ROW
) AS frame_values
FROM wf_frame
ORDER BY
part_key ASC,
value ASC;
┌─part_key─┬─value─┬─order─┬─frame_values─┐
│ 1 │ 1 │ 1 │ [1] │
│ 1 │ 2 │ 2 │ [1,2] │
│ 1 │ 3 │ 3 │ [1,2,3] │
│ 1 │ 4 │ 4 │ [1,2,3,4] │
│ 1 │ 5 │ 5 │ [1,2,3,4,5] │
└──────────┴───────┴───────┴──────────────┘-- short form (frame is bounded by the beginning of a partition and the current row)
SELECT
part_key,
value,
order,
groupArray(value) OVER (PARTITION BY part_key ORDER BY order ASC) AS frame_values
FROM wf_frame
ORDER BY
part_key ASC,
value ASC;
┌─part_key─┬─value─┬─order─┬─frame_values─┐
│ 1 │ 1 │ 1 │ [1] │
│ 1 │ 2 │ 2 │ [1,2] │
│ 1 │ 3 │ 3 │ [1,2,3] │
│ 1 │ 4 │ 4 │ [1,2,3,4] │
│ 1 │ 5 │ 5 │ [1,2,3,4,5] │
└──────────┴───────┴───────┴──────────────┘-- frame is bounded by the beginning of a partition and the current row, but order is backward
SELECT
part_key,
value,
order,
groupArray(value) OVER (PARTITION BY part_key ORDER BY order DESC) AS frame_values
FROM wf_frame
ORDER BY
part_key ASC,
value ASC;
┌─part_key─┬─value─┬─order─┬─frame_values─┐
│ 1 │ 1 │ 1 │ [5,4,3,2,1] │
│ 1 │ 2 │ 2 │ [5,4,3,2] │
│ 1 │ 3 │ 3 │ [5,4,3] │
│ 1 │ 4 │ 4 │ [5,4] │
│ 1 │ 5 │ 5 │ [5] │
└──────────┴───────┴───────┴──────────────┘-- sliding frame - 1 PRECEDING ROW AND CURRENT ROW
SELECT
part_key,
value,
order,
groupArray(value) OVER (
PARTITION BY part_key
ORDER BY order ASC
Rows BETWEEN 1 PRECEDING AND CURRENT ROW
) AS frame_values
FROM wf_frame
ORDER BY
part_key ASC,
value ASC;
┌─part_key─┬─value─┬─order─┬─frame_values─┐
│ 1 │ 1 │ 1 │ [1] │
│ 1 │ 2 │ 2 │ [1,2] │
│ 1 │ 3 │ 3 │ [2,3] │
│ 1 │ 4 │ 4 │ [3,4] │
│ 1 │ 5 │ 5 │ [4,5] │
└──────────┴───────┴───────┴──────────────┘-- sliding frame - Rows BETWEEN 1 PRECEDING AND UNBOUNDED FOLLOWING
SELECT
part_key,
value,
order,
groupArray(value) OVER (
PARTITION BY part_key
ORDER BY order ASC
Rows BETWEEN 1 PRECEDING AND UNBOUNDED FOLLOWING
) AS frame_values
FROM wf_frame
ORDER BY
part_key ASC,
value ASC;
┌─part_key─┬─value─┬─order─┬─frame_values─┐
│ 1 │ 1 │ 1 │ [1,2,3,4,5] │
│ 1 │ 2 │ 2 │ [1,2,3,4,5] │
│ 1 │ 3 │ 3 │ [2,3,4,5] │
│ 1 │ 4 │ 4 │ [3,4,5] │
│ 1 │ 5 │ 5 │ [4,5] │
└──────────┴───────┴───────┴──────────────┘-- row_number does not respect the frame, so rn_1 = rn_2 = rn_3 != rn_4
SELECT
part_key,
value,
order,
groupArray(value) OVER w1 AS frame_values,
row_number() OVER w1 AS rn_1,
sum(1) OVER w1 AS rn_2,
row_number() OVER w2 AS rn_3,
sum(1) OVER w2 AS rn_4
FROM wf_frame
WINDOW
w1 AS (PARTITION BY part_key ORDER BY order DESC),
w2 AS (
PARTITION BY part_key
ORDER BY order DESC
Rows BETWEEN 1 PRECEDING AND CURRENT ROW
)
ORDER BY
part_key ASC,
value ASC;
┌─part_key─┬─value─┬─order─┬─frame_values─┬─rn_1─┬─rn_2─┬─rn_3─┬─rn_4─┐
│ 1 │ 1 │ 1 │ [5,4,3,2,1] │ 5 │ 5 │ 5 │ 2 │
│ 1 │ 2 │ 2 │ [5,4,3,2] │ 4 │ 4 │ 4 │ 2 │
│ 1 │ 3 │ 3 │ [5,4,3] │ 3 │ 3 │ 3 │ 2 │
│ 1 │ 4 │ 4 │ [5,4] │ 2 │ 2 │ 2 │ 2 │
│ 1 │ 5 │ 5 │ [5] │ 1 │ 1 │ 1 │ 1 │
└──────────┴───────┴───────┴──────────────┴──────┴──────┴──────┴──────┘-- first_value and last_value respect the frame
SELECT
groupArray(value) OVER w1 AS frame_values_1,
first_value(value) OVER w1 AS first_value_1,
last_value(value) OVER w1 AS last_value_1,
groupArray(value) OVER w2 AS frame_values_2,
first_value(value) OVER w2 AS first_value_2,
last_value(value) OVER w2 AS last_value_2
FROM wf_frame
WINDOW
w1 AS (PARTITION BY part_key ORDER BY order ASC),
w2 AS (PARTITION BY part_key ORDER BY order ASC Rows BETWEEN 1 PRECEDING AND CURRENT ROW)
ORDER BY
part_key ASC,
value ASC;
┌─frame_values_1─┬─first_value_1─┬─last_value_1─┬─frame_values_2─┬─first_value_2─┬─last_value_2─┐
│ [1] │ 1 │ 1 │ [1] │ 1 │ 1 │
│ [1,2] │ 1 │ 2 │ [1,2] │ 1 │ 2 │
│ [1,2,3] │ 1 │ 3 │ [2,3] │ 2 │ 3 │
│ [1,2,3,4] │ 1 │ 4 │ [3,4] │ 3 │ 4 │
│ [1,2,3,4,5] │ 1 │ 5 │ [4,5] │ 4 │ 5 │
└────────────────┴───────────────┴──────────────┴────────────────┴───────────────┴──────────────┘-- second value within the frame
SELECT
groupArray(value) OVER w1 AS frame_values_1,
nth_value(value, 2) OVER w1 AS second_value
FROM wf_frame
WINDOW w1 AS (PARTITION BY part_key ORDER BY order ASC Rows BETWEEN 3 PRECEDING AND CURRENT ROW)
ORDER BY
part_key ASC,
value ASC
┌─frame_values_1─┬─second_value─┐
│ [1] │ 0 │
│ [1,2] │ 2 │
│ [1,2,3] │ 2 │
│ [1,2,3,4] │ 2 │
│ [2,3,4,5] │ 3 │
└────────────────┴──────────────┘-- second value within the frame + Null for missing values
SELECT
groupArray(value) OVER w1 AS frame_values_1,
nth_value(toNullable(value), 2) OVER w1 AS second_value
FROM wf_frame
WINDOW w1 AS (PARTITION BY part_key ORDER BY order ASC Rows BETWEEN 3 PRECEDING AND CURRENT ROW)
ORDER BY
part_key ASC,
value ASC
┌─frame_values_1─┬─second_value─┐
│ [1] │ ᴺᵁᴸᴸ │
│ [1,2] │ 2 │
│ [1,2,3] │ 2 │
│ [1,2,3,4] │ 2 │
│ [2,3,4,5] │ 3 │
└────────────────┴──────────────┘
Real world examples
The following examples solve common real-world problems.
Maximum/total salary per department
CREATE TABLE employees
(
`department` String,
`employee_name` String,
`salary` Float
)
ENGINE = Memory;
INSERT INTO employees FORMAT Values
('Finance', 'Jonh', 200),
('Finance', 'Joan', 210),
('Finance', 'Jean', 505),
('IT', 'Tim', 200),
('IT', 'Anna', 300),
('IT', 'Elen', 500);SELECT
department,
employee_name AS emp,
salary,
max_salary_per_dep,
total_salary_per_dep,
round((salary / total_salary_per_dep) * 100, 2) AS `share_per_dep(%)`
FROM
(
SELECT
department,
employee_name,
salary,
max(salary) OVER wndw AS max_salary_per_dep,
sum(salary) OVER wndw AS total_salary_per_dep
FROM employees
WINDOW wndw AS (
PARTITION BY department
rows BETWEEN UNBOUNDED PRECEDING AND UNBOUNDED FOLLOWING
)
ORDER BY
department ASC,
employee_name ASC
);
┌─department─┬─emp──┬─salary─┬─max_salary_per_dep─┬─total_salary_per_dep─┬─share_per_dep(%)─┐
│ Finance │ Jean │ 505 │ 505 │ 915 │ 55.19 │
│ Finance │ Joan │ 210 │ 505 │ 915 │ 22.95 │
│ Finance │ Jonh │ 200 │ 505 │ 915 │ 21.86 │
│ IT │ Anna │ 300 │ 500 │ 1000 │ 30 │
│ IT │ Elen │ 500 │ 500 │ 1000 │ 50 │
│ IT │ Tim │ 200 │ 500 │ 1000 │ 20 │
└────────────┴──────┴────────┴────────────────────┴──────────────────────┴──────────────────┘
Cumulative sum
CREATE TABLE warehouse
(
`item` String,
`ts` DateTime,
`value` Float
)
ENGINE = Memory
INSERT INTO warehouse VALUES
('sku38', '2020-01-01', 9),
('sku38', '2020-02-01', 1),
('sku38', '2020-03-01', -4),
('sku1', '2020-01-01', 1),
('sku1', '2020-02-01', 1),
('sku1', '2020-03-01', 1);SELECT
item,
ts,
value,
sum(value) OVER (PARTITION BY item ORDER BY ts ASC) AS stock_balance
FROM warehouse
ORDER BY
item ASC,
ts ASC;
┌─item──┬──────────────────ts─┬─value─┬─stock_balance─┐
│ sku1 │ 2020-01-01 00:00:00 │ 1 │ 1 │
│ sku1 │ 2020-02-01 00:00:00 │ 1 │ 2 │
│ sku1 │ 2020-03-01 00:00:00 │ 1 │ 3 │
│ sku38 │ 2020-01-01 00:00:00 │ 9 │ 9 │
│ sku38 │ 2020-02-01 00:00:00 │ 1 │ 10 │
│ sku38 │ 2020-03-01 00:00:00 │ -4 │ 6 │
└───────┴─────────────────────┴───────┴───────────────┘
Moving / Sliding Average (per 3 rows)
CREATE TABLE sensors
(
`metric` String,
`ts` DateTime,
`value` Float
)
ENGINE = Memory;
insert into sensors values('cpu_temp', '2020-01-01 00:00:00', 87),
('cpu_temp', '2020-01-01 00:00:01', 77),
('cpu_temp', '2020-01-01 00:00:02', 93),
('cpu_temp', '2020-01-01 00:00:03', 87),
('cpu_temp', '2020-01-01 00:00:04', 87),
('cpu_temp', '2020-01-01 00:00:05', 87),
('cpu_temp', '2020-01-01 00:00:06', 87),
('cpu_temp', '2020-01-01 00:00:07', 87);SELECT
metric,
ts,
value,
avg(value) OVER (
PARTITION BY metric
ORDER BY ts ASC
Rows BETWEEN 2 PRECEDING AND CURRENT ROW
) AS moving_avg_temp
FROM sensors
ORDER BY
metric ASC,
ts ASC;
┌─metric───┬──────────────────ts─┬─value─┬───moving_avg_temp─┐
│ cpu_temp │ 2020-01-01 00:00:00 │ 87 │ 87 │
│ cpu_temp │ 2020-01-01 00:00:01 │ 77 │ 82 │
│ cpu_temp │ 2020-01-01 00:00:02 │ 93 │ 85.66666666666667 │
│ cpu_temp │ 2020-01-01 00:00:03 │ 87 │ 85.66666666666667 │
│ cpu_temp │ 2020-01-01 00:00:04 │ 87 │ 89 │
│ cpu_temp │ 2020-01-01 00:00:05 │ 87 │ 87 │
│ cpu_temp │ 2020-01-01 00:00:06 │ 87 │ 87 │
│ cpu_temp │ 2020-01-01 00:00:07 │ 87 │ 87 │
└──────────┴─────────────────────┴───────┴───────────────────┘
Moving / Sliding Average (per 10 seconds)
SELECT
metric,
ts,
value,
avg(value) OVER (PARTITION BY metric ORDER BY ts
Range BETWEEN 10 PRECEDING AND CURRENT ROW) AS moving_avg_10_seconds_temp
FROM sensors
ORDER BY
metric ASC,
ts ASC;
┌─metric───┬──────────────────ts─┬─value─┬─moving_avg_10_seconds_temp─┐
│ cpu_temp │ 2020-01-01 00:00:00 │ 87 │ 87 │
│ cpu_temp │ 2020-01-01 00:01:10 │ 77 │ 77 │
│ cpu_temp │ 2020-01-01 00:02:20 │ 93 │ 93 │
│ cpu_temp │ 2020-01-01 00:03:30 │ 87 │ 87 │
│ cpu_temp │ 2020-01-01 00:04:40 │ 87 │ 87 │
│ cpu_temp │ 2020-01-01 00:05:50 │ 87 │ 87 │
│ cpu_temp │ 2020-01-01 00:06:00 │ 87 │ 87 │
│ cpu_temp │ 2020-01-01 00:07:10 │ 87 │ 87 │
└──────────┴─────────────────────┴───────┴────────────────────────────┘
Moving / Sliding Average (per 10 days)
Temperature is stored with second precision, but using Range and ORDER BY toDate(ts) we form a frame with the size of 10 units, and because of toDate(ts) the unit is a day.
CREATE TABLE sensors
(
`metric` String,
`ts` DateTime,
`value` Float
)
ENGINE = Memory;
insert into sensors values('ambient_temp', '2020-01-01 00:00:00', 16),
('ambient_temp', '2020-01-01 12:00:00', 16),
('ambient_temp', '2020-01-02 11:00:00', 9),
('ambient_temp', '2020-01-02 12:00:00', 9),
('ambient_temp', '2020-02-01 10:00:00', 10),
('ambient_temp', '2020-02-01 12:00:00', 10),
('ambient_temp', '2020-02-10 12:00:00', 12),
('ambient_temp', '2020-02-10 13:00:00', 12),
('ambient_temp', '2020-02-20 12:00:01', 16),
('ambient_temp', '2020-03-01 12:00:00', 16),
('ambient_temp', '2020-03-01 12:00:00', 16),
('ambient_temp', '2020-03-01 12:00:00', 16);SELECT
metric,
ts,
value,
round(avg(value) OVER (PARTITION BY metric ORDER BY toDate(ts)
Range BETWEEN 10 PRECEDING AND CURRENT ROW),2) AS moving_avg_10_days_temp
FROM sensors
ORDER BY
metric ASC,
ts ASC;
┌─metric───────┬──────────────────ts─┬─value─┬─moving_avg_10_days_temp─┐
│ ambient_temp │ 2020-01-01 00:00:00 │ 16 │ 16 │
│ ambient_temp │ 2020-01-01 12:00:00 │ 16 │ 16 │
│ ambient_temp │ 2020-01-02 11:00:00 │ 9 │ 12.5 │
│ ambient_temp │ 2020-01-02 12:00:00 │ 9 │ 12.5 │
│ ambient_temp │ 2020-02-01 10:00:00 │ 10 │ 10 │
│ ambient_temp │ 2020-02-01 12:00:00 │ 10 │ 10 │
│ ambient_temp │ 2020-02-10 12:00:00 │ 12 │ 11 │
│ ambient_temp │ 2020-02-10 13:00:00 │ 12 │ 11 │
│ ambient_temp │ 2020-02-20 12:00:01 │ 16 │ 13.33 │
│ ambient_temp │ 2020-03-01 12:00:00 │ 16 │ 16 │
│ ambient_temp │ 2020-03-01 12:00:00 │ 16 │ 16 │
│ ambient_temp │ 2020-03-01 12:00:00 │ 16 │ 16 │
└──────────────┴─────────────────────┴───────┴─────────────────────────┘
References
GitHub Issues
The roadmap for the initial support of window functions is in this issue.
All GitHub issues related to window functions have the comp-window-functions tag.
Tests
These tests contain the examples of the currently supported grammar:
https://github.com/ClickHouse/ClickHouse/blob/master/tests/performance/window_functions.xml
Postgres Docs
https://www.postgresql.org/docs/current/sql-select.html#SQL-WINDOW
https://www.postgresql.org/docs/devel/sql-expressions.html#SYNTAX-WINDOW-FUNCTIONS
https://www.postgresql.org/docs/devel/functions-window.html
https://www.postgresql.org/docs/devel/tutorial-window.html
MySQL Docs
https://dev.mysql.com/doc/refman/8.0/en/window-function-descriptions.html
https://dev.mysql.com/doc/refman/8.0/en/window-functions-usage.html
https://dev.mysql.com/doc/refman/8.0/en/window-functions-frames.html