GitHub user wzhfy opened a pull request:
https://github.com/apache/spark/pull/15090
[SPARK-17073] [SQL] generate column-level statistics
## What changes were proposed in this pull request?
Generate basic column statistics for all the atomic types:
- numeric types: max, min, num of nulls, ndv (number of distinct values)
- date/timestamp types: they are also represented as numbers internally, so
they have the same stats as above.
- string: avg length, max length, num of nulls, ndv
- binary: avg length, max length, num of nulls
- boolean: num of nulls, num of trues, num of falsies, ndv (must be 2)
Also support storing and loading these statistics.
## How was this patch tested?
add unit tests
You can merge this pull request into a Git repository by running:
$ git pull https://github.com/wzhfy/spark colStats
Alternatively you can review and apply these changes as the patch at:
https://github.com/apache/spark/pull/15090.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 #15090
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commit 59ae3dfc45751705962a1370c195c67c6302c376
Author: Zhenhua Wang <wzh_...@163.com>
Date: 2016-09-14T03:03:05Z
support column-level stats
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