[Hive - LanguageManual ] Windowing and Analytics Functions （待）

LanguageManual WindowingAndAnalytics

 

 

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Windowing and Analytics Functions

 

• Windowing and Analytics Functions
  • Enhancements to Hive QL
  • Examples
    • PARTITION BY with one partitioning column, no ORDER BY or window specification
    • PARTITION BY with two partitioning columns, no ORDER BY or window specification
    • PARTITION BY with one partitioning column, one ORDER BY column, and no window specification
    • PARTITION BY with two partitioning columns, two ORDER BY columns, and no window specification
    • PARTITION BY with partitioning, ORDER BY, and window specification
    • WINDOW clause
    • LEAD using default 1 row lead and not specifying default value
    • LAG specifying a lag of 3 rows and default value of 0

 

Enhancements to Hive QL

Version

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Introduced in Hive version 0.11.

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:

1. 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
2. The OVER clause
   • OVER with standard aggregates:
     • COUNT
     • SUM
     • MIN
     • MAX
     • AVG
   • 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.

     • OVER with a window specification. Windows can be defined separately in a WINDOW clause. Window specifications support these standard options:

       ROWS ((CURRENT ROW) | (UNBOUNDED | [num]) PRECEDING) AND (UNBOUNDED | [num]) FOLLOWING
       

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       The OVER clause supports the following functions, but it does not support a window with them (see HIVE-4797):

       Ranking functions: Rank, NTile, DenseRank, CumeDist, PercentRank.

       Lead and Lag functions.

3. 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;

PARTITION BY with two partitioning columns, no ORDER BY or window specification

SELECT  a,  COUNT (b) OVER (PARTITION  BY  c, d) FROM  T;

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;

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;

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;

SELECT  a,  AVG (b) OVER (PARTITION  BY  c  ORDER  BY  d  ROWS  BETWEEN  3 PRECEDING  AND  CURRENT  ROW) FROM  T;

SELECT  a,  AVG (b) OVER (PARTITION  BY  c  ORDER  BY  d  ROWS  BETWEEN  3 PRECEDING  AND  3 FOLLOWING) FROM  T;

SELECT  a,  AVG (b) OVER (PARTITION  BY  c  ORDER  BY  d  ROWS  BETWEEN  CURRENT  ROW  AND  UNBOUNDED FOLLOWING) FROM  T;

 

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;

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;

WINDOW clause

SELECT  a,  SUM (b) OVER w FROM  T; WINDOW w  AS  (PARTITION  BY  c  ORDER  BY  d  ROWS  UNBOUNDED PRECEDING)

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;

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;

 

转载于:https://www.cnblogs.com/tmeily/p/4249962.html