GitHub user sirpkt opened a pull request:
https://github.com/apache/tajo/pull/351
TAJO-919: Implement LAG and LEAD window functions
This patch contains following changes
- lead, lag are implemented. lag is implemented as window function as it
only sees previous rows while lead is implemented as aggregation function since
it should see next rows.
- visitWindowFunction() in ExprAnnotator.java and TypeDeterminant.java is
modified to support multiple arguments because current implementation only
supports one argument for window function.
There are some arguable points
- It assumes that offset value is non-negative.
- Way to handle aggregation function in WindowAggExec.java is modified to
call terminate for every Tuple, and it provides way to return different value
for each terminate call, which is essential to implement lead function within
current window supporting structure. However, it adds additional burden for
other aggregation functions calculation because their terminate calls always
induce the same calculation and return the same results.
- lead implementation temporarily holds all the rows in the same partition
in memory.
Any idea about above points and about other parts of the patch, please.
You can merge this pull request into a Git repository by running:
$ git pull https://github.com/sirpkt/tajo TAJO-919
Alternatively you can review and apply these changes as the patch at:
https://github.com/apache/tajo/pull/351.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 #351
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commit 59baae3cdde8d7731bfb100f4589f46ff856faa7
Author: Keuntae Park <[email protected]>
Date: 2015-01-14T06:04:17Z
Add window functions lag() and lead()
commit c382bed3e1273c54185cb1b4168291b7307099e6
Author: Keuntae Park <[email protected]>
Date: 2015-01-14T08:36:49Z
add support for default value on lead, lag
commit 89b76319aa6d28abc1972e920407cb2cd1ed599b
Author: Keuntae Park <[email protected]>
Date: 2015-01-14T23:34:16Z
lead, lag without argument and with default value
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