[HIVE-7650] Constant Folding performs partial evaluation on Coalesce operator

• Type: Bug
• Status: Open
• Priority: Major
• Resolution: Unresolved
• Assignee: Unassigned
• Reporter: Hari Sankar Sivarama Subramaniyan
• Created: 07/Aug/14 21:16
• Updated: 07/Aug/14 21:16

Description

EXPLAIN SELECT ctinyint, cdouble, cint, coalesce(ctinyint+10, (cdouble+log2(cint)), 0)
FROM alltypesorc
WHERE (ctinyint IS NULL) LIMIT 10;

SELECT ctinyint, cdouble, cint, coalesce(ctinyint+10, (cdouble+log2(cint)), 0)
FROM alltypesorc
WHERE (ctinyint IS NULL) LIMIT 10;

STAGE DEPENDENCIES:
Stage-1 is a root stage
Stage-0 depends on stages: Stage-1

STAGE PLANS:
Stage: Stage-1
Map Reduce
Map Operator Tree:
TableScan
alias: alltypesorc
Statistics: Num rows: 165041 Data size: 2640659 Basic stats: COMPLETE Column stats: NONE
Filter Operator
predicate: ctinyint is null (type: boolean)
Statistics: Num rows: 82520 Data size: 1320321 Basic stats: COMPLETE Column stats: NONE
Select Operator
expressions: null (type: void), cdouble (type: double), cint (type: int), COALESCE((null + 10),(cdouble + log2(cint)),0) (type: double)
outputColumnNames: _col0, _col1, _col2, _col3
Statistics: Num rows: 82520 Data size: 1320321 Basic stats: COMPLETE Column stats: NONE
Limit
Number of rows: 10
Statistics: Num rows: 10 Data size: 160 Basic stats: COMPLETE Column stats: NONE
File Output Operator
compressed: false
Statistics: Num rows: 10 Data size: 160 Basic stats: COMPLETE Column stats: NONE
table:
input format: org.apache.hadoop.mapred.TextInputFormat
output format: org.apache.hadoop.hive.ql.io.HiveIgnoreKeyTextOutputFormat
serde: org.apache.hadoop.hive.serde2.lazy.LazySimpleSerDe

Stage: Stage-0
Fetch Operator
limit: 10
Processor Tree:
ListSink

As you see in the above plan, COALESCE((null + 10) can further be evaluated to null. Currently constant folding fails to perform this recursive folding.