asolimando commented on a change in pull request #3033:
URL: https://github.com/apache/hive/pull/3033#discussion_r813007732
##########
File path: ql/src/test/results/clientpositive/llap/subquery_scalar.q.out
##########
@@ -491,25 +484,25 @@ STAGE PLANS:
aggregations: count(VALUE._col0)
mode: mergepartial
outputColumnNames: _col0
- Statistics: Num rows: 1 Data size: 196 Basic stats: COMPLETE
Column stats: NONE
- Limit
- Number of rows: 0
- Statistics: Num rows: 0 Data size: 0 Basic stats: COMPLETE
Column stats: NONE
+ Statistics: Num rows: 1 Data size: 192 Basic stats: COMPLETE
Column stats: NONE
+ Filter Operator
+ predicate: sq_count_check(_col0) (type: boolean)
+ Statistics: Num rows: 1 Data size: 192 Basic stats: COMPLETE
Column stats: NONE
Review comment:
`HiveSortLimit(fetch=[0])` is introduced when `HiveMergeFilterRule` is
invoked here:
```
HiveFilter(condition=[false])
HiveFilter(condition=[sq_count_check($0)])
HiveAggregate(group=[{}], cnt=[COUNT()])
HiveProject(p_name=[null:VARCHAR(2147483647) CHARACTER SET "UTF-16LE"])
HiveFilter(condition=[IS NULL($1)])
HiveTableScan(table=[[default, part_null_n1]],
table:alias=[part_null_n1])
```
The empty filter is rewritten by `HiveRelBuilder` as a LIMIT(0) expression
(see
[HiveRelBuilder.java#L133](https://github.com/apache/hive/blob/1c3ecf95f94a0329626a9fe46670586e7767f014/ql/src/java/org/apache/hadoop/hive/ql/optimizer/calcite/HiveRelBuilder.java#L133)).
The "false" predicate is not pushed transitively in this case for the
Calcite implementation, so this transformation never happens, we are left with
what is the original plan after decorrelation (for that specific subtree):
```
2022-02-22T08:29:38,455 DEBUG [6a4314fb-ef37-46d8-8331-338fff02f1df main]
parse.CalcitePlanner: Plan after decorrelation:
HiveProject(p_partkey=[$0], p_name=[$1], p_mfgr=[$2], p_brand=[$3],
p_type=[$4], p_size=[$5], p_container=[$6], p_retailprice=[$7], p_comment=
[$8])
HiveProject(p_partkey=[$0], p_name=[$1], p_mfgr=[$2], p_brand=[$3],
p_type=[$4], p_size=[$5], p_container=[$6], p_retailprice=[$7], p_commen
t=[$8], BLOCK__OFFSET__INSIDE__FILE=[$9], INPUT__FILE__NAME=[$10],
ROW__ID=[$11], ROW__IS__DELETED=[$12])
HiveFilter(condition=[=($1, $14)])
HiveJoin(condition=[true], joinType=[left], algorithm=[none],
cost=[not available])
HiveJoin(condition=[true], joinType=[inner], algorithm=[none],
cost=[not available])
HiveTableScan(table=[[default, part]], table:alias=[part])
HiveFilter(condition=[sq_count_check($0)])
HiveAggregate(group=[{}], cnt=[COUNT()])
HiveProject(p_name=[$1])
HiveFilter(condition=[IS NULL($1)])
HiveTableScan(table=[[default, part_null_n1]],
table:alias=[part_null_n1])
HiveProject(p_name=[$1])
HiveFilter(condition=[IS NULL($1)])
HiveTableScan(table=[[default, part_null_n1]],
table:alias=[part_null_n1])
```
`false` predicate is not inferred in Calcite, which does not support "non
field predicates" (see
[HiveRelMdPredicates.java#L439](https://github.com/apache/hive/blob/1c3ecf95f94a0329626a9fe46670586e7767f014/ql/src/java/org/apache/hadoop/hive/ql/optimizer/calcite/stats/HiveRelMdPredicates.java#L439)),
which are predicates without field reference in it.
I will see if I can craft a similar query for Calcite and file an
improvement ticket to support such predicates without field reference.
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