[DRILL-4476] Enhance Union-All operator for dealing with empty left input or empty both inputs

• Type: Bug
• Status: Resolved
• Priority: Major
• Resolution: Fixed
• Fix Version/s: 1.7.0
• Component/s: Execution - Relational Operators
• Assignee: Sean Hsuan-Yi Chu
• Reporter: Sean Hsuan-Yi Chu
• Reviewer: Khurram Faraaz
• Created: 04/Mar/16 23:21
• Updated: 26/May/17 20:45
• Resolved: 13/Mar/16 18:43

Description

Union-All operator does not deal with the situation where left side comes from empty source.

Due to DRILL-2288's enhancement for empty sources, Union-All operator now can be allowed to support this scenario.

Issue Links

• incorporates: DRILL-4472 Pushing Filter past Union All fails: DRILL-3257 regressed DRILL-2746 but unit test update break test goal
• is related to: DRILL-5327 Hash aggregate can return empty batch which can cause schema change exception
• is related to: DRILL-5546 Schema change problems caused by empty batch
• is related to: DRILL-2288 ScanBatch violates IterOutcome protocol for zero-row sources [was: missing JDBC metadata (schema) for 0-row results...]
• relates to: DRILL-4510 IllegalStateException: Failure while reading vector. Expected vector class of org.apache.drill.exec.vector.NullableIntVector but was holding vector class org.apache.drill.exec.vector.NullableVarCharVector