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From "Davies Liu (JIRA)" <j...@apache.org>
Subject [jira] [Updated] (SPARK-17845) Improve window function frame boundary API in DataFrame
Date Wed, 12 Oct 2016 23:47:20 GMT

     [ https://issues.apache.org/jira/browse/SPARK-17845?page=com.atlassian.jira.plugin.system.issuetabpanels:all-tabpanel
]

Davies Liu updated SPARK-17845:
-------------------------------
    Fix Version/s: 2.1.0

> Improve window function frame boundary API in DataFrame
> -------------------------------------------------------
>
>                 Key: SPARK-17845
>                 URL: https://issues.apache.org/jira/browse/SPARK-17845
>             Project: Spark
>          Issue Type: Improvement
>          Components: SQL
>            Reporter: Reynold Xin
>            Assignee: Reynold Xin
>             Fix For: 2.1.0
>
>
> ANSI SQL uses the following to specify the frame boundaries for window functions:
> {code}
> ROWS BETWEEN 3 PRECEDING AND 3 FOLLOWING
> ROWS BETWEEN UNBOUNDED PRECEDING AND 3 PRECEDING
> ROWS BETWEEN UNBOUNDED PRECEDING AND CURRENT ROW
> ROWS BETWEEN CURRENT ROW AND UNBOUNDED PRECEDING
> ROWS BETWEEN UNBOUNDED PRECEDING AND UNBOUNDED FOLLOWING
> {code}
> In Spark's DataFrame API, we use integer values to indicate relative position:
> - 0 means "CURRENT ROW"
> - -1 means "1 PRECEDING"
> - Long.MinValue means "UNBOUNDED PRECEDING"
> - Long.MaxValue to indicate "UNBOUNDED FOLLOWING"
> {code}
> // ROWS BETWEEN 3 PRECEDING AND 3 FOLLOWING
> Window.rowsBetween(-3, +3)
> // ROWS BETWEEN UNBOUNDED PRECEDING AND 3 PRECEDING
> Window.rowsBetween(Long.MinValue, -3)
> // ROWS BETWEEN UNBOUNDED PRECEDING AND CURRENT ROW
> Window.rowsBetween(Long.MinValue, 0)
> // ROWS BETWEEN CURRENT ROW AND UNBOUNDED PRECEDING
> Window.rowsBetween(0, Long.MaxValue)
> // ROWS BETWEEN UNBOUNDED PRECEDING AND UNBOUNDED FOLLOWING
> Window.rowsBetween(Long.MinValue, Long.MaxValue)
> {code}
> I think using numeric values to indicate relative positions is actually a good idea,
but the reliance on Long.MinValue and Long.MaxValue to indicate unbounded ends is pretty confusing:
> 1. The API is not self-evident. There is no way for a new user to figure out how to indicate
an unbounded frame by looking at just the API. The user has to read the doc to figure this
out.
> 2. It is weird Long.MinValue or Long.MaxValue has some special meaning.
> 3. Different languages have different min/max values, e.g. in Python we use -sys.maxsize
and +sys.maxsize.
> To make this API less confusing, we have a few options:
> Option 1. Add the following (additional) methods:
> {code}
> // ROWS BETWEEN 3 PRECEDING AND 3 FOLLOWING
> Window.rowsBetween(-3, +3)  // this one exists already
> // ROWS BETWEEN UNBOUNDED PRECEDING AND 3 PRECEDING
> Window.rowsBetweenUnboundedPrecedingAnd(-3)
> // ROWS BETWEEN UNBOUNDED PRECEDING AND CURRENT ROW
> Window.rowsBetweenUnboundedPrecedingAndCurrentRow()
> // ROWS BETWEEN CURRENT ROW AND UNBOUNDED PRECEDING
> Window.rowsBetweenCurrentRowAndUnboundedFollowing()
> // ROWS BETWEEN UNBOUNDED PRECEDING AND UNBOUNDED FOLLOWING
> Window.rowsBetweenUnboundedPrecedingAndUnboundedFollowing()
> {code}
> This is obviously very verbose, but is very similar to how these functions are done in
SQL, and is perhaps the most obvious to end users, especially if they come from SQL background.
> Option 2. Decouple the specification for frame begin and frame end into two functions.
Assume the boundary is unlimited unless specified.
> {code}
> // ROWS BETWEEN 3 PRECEDING AND 3 FOLLOWING
> Window.rowsFrom(-3).rowsTo(3)
> // ROWS BETWEEN UNBOUNDED PRECEDING AND 3 PRECEDING
> Window.rowsTo(-3)
> // ROWS BETWEEN UNBOUNDED PRECEDING AND CURRENT ROW
> Window.rowsToCurrent() or Window.rowsTo(0)
> // ROWS BETWEEN CURRENT ROW AND UNBOUNDED PRECEDING
> Window.rowsFromCurrent() or Window.rowsFrom(0)
> // ROWS BETWEEN UNBOUNDED PRECEDING AND UNBOUNDED FOLLOWING
> // no need to specify
> {code}
> If we go with option 2, we should throw exceptions if users specify multiple from's or
to's. A variant of option 2 is to require explicitly specification of begin/end even in the
case of unbounded boundary, e.g.:
> {code}
> Window.rowsFromBeginning().rowsTo(-3)
> or
> Window.rowsFromUnboundedPreceding().rowsTo(-3)
> {code}



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