GitHub user xwu0226 opened a pull request:
https://github.com/apache/spark/pull/14842
[SPARK-10747][SQL] Support NULS FIRST|LAST clause in ORDER BY
## What changes were proposed in this pull request?
Currently, ORDER BY clause returns nulls value according to sorting order
(ASC|DESC), considering null value is always smaller than non-null values.
However, SQL2003 standard support NULLS FIRST or NULLS LAST to allow users
to specify whether null values should be returned first or last, regardless of
sorting order (ASC|DESC).
This PR is to support this new feature.
## How was this patch tested?
New test cases are added to test NULLS FIRST|LAST for regular select
queries and windowing queries.
(If this patch involves UI changes, please attach a screenshot; otherwise,
remove this)
You can merge this pull request into a Git repository by running:
$ git pull https://github.com/xwu0226/spark SPARK-10747
Alternatively you can review and apply these changes as the patch at:
https://github.com/apache/spark/pull/14842.patch
To close this pull request, make a commit to your master/trunk branch
with (at least) the following in the commit message:
This closes #14842
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commit 91e40fdecbc2493f1c98b8d49a6ae1b70850ea5f
Author: Xin Wu <[email protected]>
Date: 2016-08-18T16:48:59Z
initial change
commit f3fbc8810d81903c874b7416232df565496239d6
Author: Xin Wu <[email protected]>
Date: 2016-08-18T22:48:49Z
SPARK-10747: support NULLS FIRST|LAST in ORDER BY clause
commit 7dd8da23cd81ad0c85d681a667e69536e2c18b55
Author: Xin Wu <[email protected]>
Date: 2016-08-19T19:38:17Z
SPARK-10747: add testcases
commit f8f2b82643948c5a5bcd5947889052e8fd066d95
Author: Xin Wu <[email protected]>
Date: 2016-08-20T04:10:37Z
SPARK-10747: update testcases
commit a8689e0a0ebc77f625489f7154099a129b6b0283
Author: Xin Wu <[email protected]>
Date: 2016-08-26T17:59:20Z
SPARK-10747: prefix comparator enhancement to support nulls last/first
commit 267159bbd4d5a4bd1dcf919572cc197032c549a4
Author: Xin Wu <[email protected]>
Date: 2016-08-27T02:20:38Z
SPARK-10747: refine prefix comparator
commit 760e890b7ca43070dff1f5df4173750ed65454a1
Author: Xin Wu <[email protected]>
Date: 2016-08-27T04:06:46Z
SPARK-10747: add testcases
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