[SPARK-6040][SQL] Fix the percent bug in tablesample

[watermen]

HiveQL expression like select count(1) from src tablesample(1 percent); means take 1% sample to select. But it means 100% in the current version of the Spark.

[AmplabJenkins]

Can one of the admins verify this patch?

[yhuai]

test this please

[SparkQA]

Test build #28014 has started for PR 4789 at commit 92cbc4a.

• This patch merges cleanly.

[SparkQA]

Test build #28014 has finished for PR 4789 at commit 92cbc4a.

• This patch fails Scala style tests.
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• This patch adds no public classes.

[AmplabJenkins]

Test FAILed.
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Test FAILed.

[scwf]

test this please

[watermen]

@yhuai Can you trigger the test for me?

[chenghao-intel]

retest this please

[yhuai]

ok to test

[SparkQA]

Test build #28153 has started for PR 4789 at commit 01abcce.

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[SparkQA]

Test build #28153 has finished for PR 4789 at commit 01abcce.

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• This patch adds no public classes.

[AmplabJenkins]

Test PASSed.
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[yhuai]

How about "The range of fraction accepted by Sample is [0, 1]. Because Hive's block sampling function takes X PERCENT as the input and the range of X is [0, 100], we need to adjust the fraction."?

[watermen]

@yhuai Thanks for you help and I had done it.

[SparkQA]

Test build #28160 has started for PR 4789 at commit 2453ebe.

• This patch merges cleanly.

[SparkQA]

Test build #28160 has finished for PR 4789 at commit 2453ebe.

• This patch passes all tests.
• This patch merges cleanly.
• This patch adds no public classes.

[AmplabJenkins]

Test PASSed.
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Test PASSed.

[marmbrus]

I'm going to go ahead and merge this since it changes semantics and we are close to the release where we remove the alpha tag, but it would be great if you could add a test that actually checks to make sure sampling is happening and we are getting something close to the expected number of results.