[HIVE-12735] Constant folding for WHEN/CASE expression does not set return type correctly

• Type: Bug
• Status: Closed
• Priority: Major
• Resolution: Fixed
• Affects Version/s: 1.3.0, 2.0.0, 2.1.0
• Fix Version/s: 1.3.0, 2.0.0
• Component/s: Logical Optimizer
• Assignee: Prasanth Jayachandran
• Reporter: Prasanth Jayachandran
• Created: 23/Dec/15 00:23
• Updated: 14/Jan/22 14:45
• Resolved: 24/Dec/15 03:08

Description

For the following query

SELECT IF ( ( (CASE WHEN bool0 THEN 1 WHEN NOT bool0 THEN 0 END) = (CASE WHEN TRUE THEN 1 WHEN NOT TRUE THEN 0 END) ), key0, IF ( ( (CASE WHEN bool0 THEN 1 WHEN NOT bool0 THEN 0 END) = (CASE WHEN FALSE THEN 1 WHEN NOT FALSE THEN 0 END) ), key1, key2 ) ) FROM src_orc;

the expression gets constant folded to

if(CASE WHEN (bool0) THEN (true) WHEN ((not bool0)) THEN (false) END, key0, if(CASE WHEN (bool0) THEN (false) WHEN ((not bool0)) THEN (true) END, key1, key2)) (type: string)

however, the GenericUDFWhen and GenericUDFCase expression retain the original return type (int) instead of the folded return type (boolean). This can cause ClassCastException for the above query when vectorization is enabled.
Following is the exception

Caused by: org.apache.hadoop.hive.ql.metadata.HiveException: Error evaluating if(CASE WHEN (bool0) THEN (true) WHEN ((not bool0)) THEN (false) END, key0, if(CASE WHEN (bool0) THEN (false) WHEN ((not bool0)) THEN (true) END, key1, key2))
	at org.apache.hadoop.hive.ql.exec.vector.VectorSelectOperator.process(VectorSelectOperator.java:126)
	at org.apache.hadoop.hive.ql.exec.Operator.forward(Operator.java:852)
	at org.apache.hadoop.hive.ql.exec.TableScanOperator.process(TableScanOperator.java:114)
	at org.apache.hadoop.hive.ql.exec.MapOperator$MapOpCtx.forward(MapOperator.java:168)
	at org.apache.hadoop.hive.ql.exec.vector.VectorMapOperator.process(VectorMapOperator.java:45)
	... 18 more
Caused by: java.lang.ClassCastException: org.apache.hadoop.io.BooleanWritable cannot be cast to org.apache.hadoop.io.IntWritable
	at org.apache.hadoop.hive.serde2.objectinspector.primitive.WritableIntObjectInspector.get(WritableIntObjectInspector.java:36)
	at org.apache.hadoop.hive.ql.exec.vector.udf.VectorUDFAdaptor.setOutputCol(VectorUDFAdaptor.java:262)
	at org.apache.hadoop.hive.ql.exec.vector.udf.VectorUDFAdaptor.setResult(VectorUDFAdaptor.java:210)
	at org.apache.hadoop.hive.ql.exec.vector.udf.VectorUDFAdaptor.evaluate(VectorUDFAdaptor.java:140)
	at org.apache.hadoop.hive.ql.exec.vector.expressions.VectorExpression.evaluateChildren(VectorExpression.java:121)
	at org.apache.hadoop.hive.ql.exec.vector.expressions.IfExprStringGroupColumnStringGroupColumn.evaluate(IfExprStringGroupColumnStringGroupColumn.java:54)
	at org.apache.hadoop.hive.ql.exec.vector.VectorSelectOperator.process(VectorSelectOperator.java:123)
	... 22 more

Issue Links

• is duplicated by: HIVE-25861 When ConstantPropagate optimizer optimizes case when equals case when twice, got wrong logical execution plan
• is related to: HIVE-9644 Fold case & when udfs
• links to: RB