Windowing and Analytics Functions
Enhancements to Hive QL
This section introduces the Hive QL enhancements for windowing and analytics functions. See "Windowing Specifications in HQL" (attached to HIVE-4197) for details. HIVE-896 has more information, including links to earlier documentation in the initial comments.
All of the windowing and analytics functions operate as per the SQL standard.
The current release supports the following functions for windowing and analytics:
- Windowing functions
- LEAD
- The number of rows to lead can optionally be specified. If the number of rows to lead is not specified, the lead is one row.
- Returns null when the lead for the current row extends beyond the end of the window.
- LAG
- The number of rows to lag can optionally be specified. If the number of rows to lag is not specified, the lag is one row.
- Returns null when the lag for the current row extends before the beginning of the window.
- FIRST_VALUE
- LAST_VALUE
- The OVER clause
- OVER with standard aggregates:
- OVER with a PARTITION BY statement with one or more partitioning columns of any primitive datatype.
- OVER with PARTITION BY and ORDER BY with one or more partitioning and/or ordering columns of any datatype.
- Analytics functions
- RANK
- ROW_NUMBER
- DENSE_RANK
- CUME_DIST
- PERCENT_RANK
- NTILE
Examples
This section provides examples of how to use the Hive QL windowing and analytics functions in SELECT statements. See HIVE-896 for additional examples.
PARTITION BY with one partitioning column, no ORDER BY or window specification
SELECT a, COUNT(b) OVER (PARTITION BY c)
FROM T;
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PARTITION BY with two partitioning columns, no ORDER BY or window specification
SELECT a, COUNT(b) OVER (PARTITION BY c, d)
FROM T;
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PARTITION BY with one partitioning column, one ORDER BY column, and no window specification
SELECT a, SUM(b) OVER (PARTITION BY c ORDER BY d)
FROM T;
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PARTITION BY with two partitioning columns, two ORDER BY columns, and no window specification
SELECT a, SUM(b) OVER (PARTITION BY c, d ORDER BY e, f)
FROM T;
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PARTITION BY with partitioning, ORDER BY, and window specification
SELECT a, SUM(b) OVER (PARTITION BY c ORDER BY d ROWS BETWEEN UNBOUNDED PRECEDING AND CURRENT ROW)
FROM T;
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SELECT a, AVG(b) OVER (PARTITION BY c ORDER BY d ROWS BETWEEN 3 PRECEDING AND CURRENT ROW)
FROM T;
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SELECT a, AVG(b) OVER (PARTITION BY c ORDER BY d ROWS BETWEEN 3 PRECEDING AND 3 FOLLOWING)
FROM T;
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SELECT a, AVG(b) OVER (PARTITION BY c ORDER BY d ROWS BETWEEN CURRENT ROW AND UNBOUNDED FOLLOWING)
FROM T;
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There can be multiple OVER clauses in a single query. A single OVER clause only applies to the immediately preceding function call. In this example, the first OVER clause applies to COUNT(b) and the second OVER clause applies to SUM(b):
SELECT
a,
COUNT(b) OVER (PARTITION BY c),
SUM(b) OVER (PARTITION BY c)
FROM T;
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Aliases can be used as well, with or without the keyword AS:
SELECT
a,
COUNT(b) OVER (PARTITION BY c) AS b_count,
SUM(b) OVER (PARTITION BY c) b_sum
FROM T;
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WINDOW clause
SELECT a, SUM(b) OVER w
FROM T;
WINDOW w AS (PARTITION BY c ORDER BY d ROWS UNBOUNDED PRECEDING)
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LEAD using default 1 row lead and not specifying default value
SELECT a, LEAD(a) OVER (PARTITION BY b ORDER BY C ROWS BETWEEN CURRENT ROW AND 1 FOLLOWING)
FROM T;
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LAG specifying a lag of 3 rows and default value of 0
SELECT a, LAG(a, 3, 0) OVER (PARTITION BY b ORDER BY C ROWS 3 PRECEDING)
FROM T;
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