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 [ nulls_option ] 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 | NTH_VALUE | FIRST_VALUE | LAST_VALUE
-
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.
-
-
nulls_option
Specifies whether or not to skip null values when evaluating the window function.
RESECT NULLS
means not skipping null values, whileIGNORE NULLS
means skipping. If not specified, the default isRESECT NULLS
.Syntax:
{ IGNORE | RESPECT } NULLS
Note: Only
LAG | LEAD | NTH_VALUE | FIRST_VALUE | LAST_VALUE
can be used withIGNORE NULLS
. -
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, salary, 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, salary, 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|
+-----+-----------+------+-----+-----+
SELECT id, v,
LEAD(v, 0) IGNORE NULLS OVER w lead,
LAG(v, 0) IGNORE NULLS OVER w lag,
NTH_VALUE(v, 2) IGNORE NULLS OVER w nth_value,
FIRST_VALUE(v) IGNORE NULLS OVER w first_value,
LAST_VALUE(v) IGNORE NULLS OVER w last_value
FROM test_ignore_null
WINDOW w AS (ORDER BY id)
ORDER BY id;
+--+----+----+----+---------+-----------+----------+
|id| v|lead| lag|nth_value|first_value|last_value|
+--+----+----+----+---------+-----------+----------+
| 0|NULL|NULL|NULL| NULL| NULL| NULL|
| 1| x| x| x| NULL| x| x|
| 2|NULL|NULL|NULL| NULL| x| x|
| 3|NULL|NULL|NULL| NULL| x| x|
| 4| y| y| y| y| x| y|
| 5|NULL|NULL|NULL| y| x| y|
| 6| z| z| z| y| x| z|
| 7| v| v| v| y| x| v|
| 8|NULL|NULL|NULL| y| x| v|
+--+----+----+----+---------+-----------+----------+