GitHub user gatorsmile opened a pull request:
https://github.com/apache/spark/pull/12838
[SPARK-15056] [SQL] Parse Unsupported Sampling Syntax and Issue Better
Exceptions
#### What changes were proposed in this pull request?
Compared with the current Spark parser, there are two extra syntax are
supported in Hive for sampling
- In `On` clauses, `rand()` is used for indicating sampling on the entire
row instead of an individual column. For example,
```SQL
SELECT * FROM source TABLESAMPLE(BUCKET 3 OUT OF 32 ON rand()) s;
```
- Users can specify the total length to be read. For example,
```SQL
SELECT * FROM source TABLESAMPLE(100M) s;
```
Below is the link for references:
https://cwiki.apache.org/confluence/display/Hive/LanguageManual+Sampling
This PR is to parse and capture these two extra syntax, and issue a better
error message.
#### How was this patch tested?
Added test cases to verify the thrown exceptions
You can merge this pull request into a Git repository by running:
$ git pull https://github.com/gatorsmile/spark bucketOnRand
Alternatively you can review and apply these changes as the patch at:
https://github.com/apache/spark/pull/12838.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 #12838
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