[CALCITE-5916] In RelBuilder, add sample() method (equivalent to SQL TABLESAMPLE clause)

• Type: Bug
• Status: Closed
• Priority: Major
• Resolution: Fixed
• Fix Version/s: 1.36.0
• Assignee: Julian Hyde
• Reporter: Julian Hyde
• Created: 10/Aug/23 18:52
• Updated: 10/Nov/23 11:34
• Resolved: 12/Aug/23 20:53

Description

In RelBuilder, add sample() method (equivalent to SQL TABLESAMPLE clause).

In SqlToRelConverter, the code

if (tableSampleSpec.getSamplePercentage() == 0f) {
  bb.setRoot(relBuilder.push(bb.root()).empty().build(), true);
} else {
  RelOptSamplingParameters params =
      new RelOptSamplingParameters(
          tableSampleSpec.isBernoulli(),
          tableSampleSpec.getSamplePercentage(),
          tableSampleSpec.isRepeatable(),
          tableSampleSpec.getRepeatableSeed());
  bb.setRoot(new Sample(cluster, bb.root(), params), false);
}

would become

relBuilder.push(bb.root());
relBuilder.sample(tableSampleSpec.isBernoulli(),
    tableSampleSpec.getSamplePercentage(),
    tableSampleSpec.isRepeatable(),
    tableSampleSpec.getRepeatableSeed());
bb.setRoot(relBuilder.build(), false);

Note that RelBuilder.sample calls empty() if the rate = 0. It should also skip sampling if rate = 1.

Issue Links

• is related to: CALCITE-5895 TABLESAMPLE(0) should return empty result
• relates to: CALCITE-5912 Add an implementation of TABLESAMPLE in Enumerable convention