Window Functions
Description
Window functions operate on a group of rows, referred to as a window, and calculate a return value for each row based on the group of rows. Window functions are useful for processing tasks such as calculating a moving average, computing a cumulative statistic, or accessing the value of rows given the relative position of the current row.
Syntax
window_function OVER
( [ { PARTITION | DISTRIBUTE } BY partition_col_name = partition_col_val ( [ , ... ] ) ]
{ ORDER | SORT } BY expression [ ASC | DESC ] [ NULLS { FIRST | LAST } ] [ , ... ]
[ window_frame ] )
Parameters
-
window_function
-
Ranking Functions
Syntax:
RANK | DENSE_RANK | PERCENT_RANK | NTILE | ROW_NUMBER
-
Analytic Functions
Syntax:
CUME_DIST | LAG | LEAD
-
Aggregate Functions
Syntax:
MAX | MIN | COUNT | SUM | AVG | ...
Please refer to the Built-in Aggregation Functions document for a complete list of Spark aggregate functions.
-
-
window_frame
Specifies which row to start the window on and where to end it.
Syntax:
{ RANGE | ROWS } { frame_start | BETWEEN frame_start AND frame_end }
-
frame_start
andframe_end
have the following syntax:Syntax:
UNBOUNDED PRECEDING | offset PRECEDING | CURRENT ROW | offset FOLLOWING | UNBOUNDED FOLLOWING
offset:
specifies theoffset
from the position of the current row.
Note: If
frame_end
is omitted it defaults toCURRENT ROW
. -
Examples
CREATE TABLE employees (name STRING, dept STRING, salary INT, age INT);
INSERT INTO employees VALUES ("Lisa", "Sales", 10000, 35);
INSERT INTO employees VALUES ("Evan", "Sales", 32000, 38);
INSERT INTO employees VALUES ("Fred", "Engineering", 21000, 28);
INSERT INTO employees VALUES ("Alex", "Sales", 30000, 33);
INSERT INTO employees VALUES ("Tom", "Engineering", 23000, 33);
INSERT INTO employees VALUES ("Jane", "Marketing", 29000, 28);
INSERT INTO employees VALUES ("Jeff", "Marketing", 35000, 38);
INSERT INTO employees VALUES ("Paul", "Engineering", 29000, 23);
INSERT INTO employees VALUES ("Chloe", "Engineering", 23000, 25);
SELECT * FROM employees;
+-----+-----------+------+-----+
| name| dept|salary| age|
+-----+-----------+------+-----+
|Chloe|Engineering| 23000| 25|
| Fred|Engineering| 21000| 28|
| Paul|Engineering| 29000| 23|
|Helen| Marketing| 29000| 40|
| Tom|Engineering| 23000| 33|
| Jane| Marketing| 29000| 28|
| Jeff| Marketing| 35000| 38|
| Evan| Sales| 32000| 38|
| Lisa| Sales| 10000| 35|
| Alex| Sales| 30000| 33|
+-----+-----------+------+-----+
SELECT name, dept, RANK() OVER (PARTITION BY dept ORDER BY salary) AS rank FROM employees;
+-----+-----------+------+----+
| name| dept|salary|rank|
+-----+-----------+------+----+
| Lisa| Sales| 10000| 1|
| Alex| Sales| 30000| 2|
| Evan| Sales| 32000| 3|
| Fred|Engineering| 21000| 1|
| Tom|Engineering| 23000| 2|
|Chloe|Engineering| 23000| 2|
| Paul|Engineering| 29000| 4|
|Helen| Marketing| 29000| 1|
| Jane| Marketing| 29000| 1|
| Jeff| Marketing| 35000| 3|
+-----+-----------+------+----+
SELECT name, dept, DENSE_RANK() OVER (PARTITION BY dept ORDER BY salary ROWS BETWEEN
UNBOUNDED PRECEDING AND CURRENT ROW) AS dense_rank FROM employees;
+-----+-----------+------+----------+
| name| dept|salary|dense_rank|
+-----+-----------+------+----------+
| Lisa| Sales| 10000| 1|
| Alex| Sales| 30000| 2|
| Evan| Sales| 32000| 3|
| Fred|Engineering| 21000| 1|
| Tom|Engineering| 23000| 2|
|Chloe|Engineering| 23000| 2|
| Paul|Engineering| 29000| 3|
|Helen| Marketing| 29000| 1|
| Jane| Marketing| 29000| 1|
| Jeff| Marketing| 35000| 2|
+-----+-----------+------+----------+
SELECT name, dept, age, CUME_DIST() OVER (PARTITION BY dept ORDER BY age
RANGE BETWEEN UNBOUNDED PRECEDING AND CURRENT ROW) AS cume_dist FROM employees;
+-----+-----------+------+------------------+
| name| dept|age | cume_dist|
+-----+-----------+------+------------------+
| Alex| Sales| 33|0.3333333333333333|
| Lisa| Sales| 35|0.6666666666666666|
| Evan| Sales| 38| 1.0|
| Paul|Engineering| 23| 0.25|
|Chloe|Engineering| 25| 0.75|
| Fred|Engineering| 28| 0.25|
| Tom|Engineering| 33| 1.0|
| Jane| Marketing| 28|0.3333333333333333|
| Jeff| Marketing| 38|0.6666666666666666|
|Helen| Marketing| 40| 1.0|
+-----+-----------+------+------------------+
SELECT name, dept, salary, MIN(salary) OVER (PARTITION BY dept ORDER BY salary) AS min
FROM employees;
+-----+-----------+------+-----+
| name| dept|salary| min|
+-----+-----------+------+-----+
| Lisa| Sales| 10000|10000|
| Alex| Sales| 30000|10000|
| Evan| Sales| 32000|10000|
|Helen| Marketing| 29000|29000|
| Jane| Marketing| 29000|29000|
| Jeff| Marketing| 35000|29000|
| Fred|Engineering| 21000|21000|
| Tom|Engineering| 23000|21000|
|Chloe|Engineering| 23000|21000|
| Paul|Engineering| 29000|21000|
+-----+-----------+------+-----+
SELECT name, salary,
LAG(salary) OVER (PARTITION BY dept ORDER BY salary) AS lag,
LEAD(salary, 1, 0) OVER (PARTITION BY dept ORDER BY salary) AS lead
FROM employees;
+-----+-----------+------+-----+-----+
| name| dept|salary| lag| lead|
+-----+-----------+------+-----+-----+
| Lisa| Sales| 10000|NULL |30000|
| Alex| Sales| 30000|10000|32000|
| Evan| Sales| 32000|30000| 0|
| Fred|Engineering| 21000| NULL|23000|
|Chloe|Engineering| 23000|21000|23000|
| Tom|Engineering| 23000|23000|29000|
| Paul|Engineering| 29000|23000| 0|
|Helen| Marketing| 29000| NULL|29000|
| Jane| Marketing| 29000|29000|35000|
| Jeff| Marketing| 35000|29000| 0|
+-----+-----------+------+-----+-----+