jayzhan211 commented on PR #15281:
URL: https://github.com/apache/datafusion/pull/15281#issuecomment-2764483579
```
statement count 0
create table t(a int, b int) as values (11, 2), (3, 0);
statement count 0
create table t2(a int, b int) as values (11, 3), (13, 1);
query IT
select e.b ,(select case when max(e2.a) > 10 then 'a' else 'b' end from t2
e2 where e2.b = e.b+1 ) from t e;
----
0 a
2 a
query TT
explain select e.b ,(select case when max(e2.a) > 10 then 'a' else 'b' end
from t2 e2 where e2.b = e.b+1 ) from t e;
----
logical_plan
01)Projection: e.b, CASE WHEN __scalar_sq_1.__always_true IS NULL THEN
Utf8("b") ELSE __scalar_sq_1.CASE WHEN max(e2.a) > Int64(10) THEN Utf8("a")
ELSE Utf8("b") END END AS CASE WHEN max(e2.a) > Int64(10) THEN Utf8("a") ELSE
Utf8("b") END
02)--Left Join: CAST(e.b AS Int64) + Int64(1) = CAST(__scalar_sq_1.b AS
Int64)
03)----SubqueryAlias: e
04)------TableScan: t projection=[b]
05)----SubqueryAlias: __scalar_sq_1
06)------Projection: CASE WHEN max(e2.a) > Int32(10) THEN Utf8("a") ELSE
Utf8("b") END AS CASE WHEN max(e2.a) > Int64(10) THEN Utf8("a") ELSE Utf8("b")
END, e2.b, Boolean(true) AS __always_true
07)--------Aggregate: groupBy=[[e2.b]], aggr=[[max(e2.a)]]
08)----------SubqueryAlias: e2
09)------------TableScan: t2 projection=[a, b]
physical_plan
01)ProjectionExec: expr=[b@0 as b, CASE WHEN __always_true@2 IS NULL THEN b
ELSE CASE WHEN max(e2.a) > Int64(10) THEN Utf8("a") ELSE Utf8("b") END@1 END as
CASE WHEN max(e2.a) > Int64(10) THEN Utf8("a") ELSE Utf8("b") END]
02)--CoalesceBatchesExec: target_batch_size=8192
03)----HashJoinExec: mode=Partitioned, join_type=Left, on=[(e.b +
Int64(1)@1, CAST(__scalar_sq_1.b AS Int64)@3)], projection=[b@0, CASE WHEN
max(e2.a) > Int64(10) THEN Utf8("a") ELSE Utf8("b") END@2, __always_true@4]
04)------CoalesceBatchesExec: target_batch_size=8192
05)--------RepartitionExec: partitioning=Hash([e.b + Int64(1)@1], 4),
input_partitions=1
06)----------ProjectionExec: expr=[b@0 as b, CAST(b@0 AS Int64) + 1 as e.b +
Int64(1)]
07)------------DataSourceExec: partitions=1, partition_sizes=[1]
08)------CoalesceBatchesExec: target_batch_size=8192
09)--------RepartitionExec: partitioning=Hash([CAST(__scalar_sq_1.b AS
Int64)@3], 4), input_partitions=4
10)----------ProjectionExec: expr=[CASE WHEN max(e2.a)@1 > 10 THEN a ELSE b
END as CASE WHEN max(e2.a) > Int64(10) THEN Utf8("a") ELSE Utf8("b") END, b@0
as b, true as __always_true, CAST(b@0 AS Int64) as CAST(__scalar_sq_1.b AS
Int64)]
11)------------AggregateExec: mode=FinalPartitioned, gby=[b@0 as b],
aggr=[max(e2.a)]
12)--------------CoalesceBatchesExec: target_batch_size=8192
13)----------------RepartitionExec: partitioning=Hash([b@0], 4),
input_partitions=4
14)------------------RepartitionExec: partitioning=RoundRobinBatch(4),
input_partitions=1
15)--------------------AggregateExec: mode=Partial, gby=[b@1 as b],
aggr=[max(e2.a)]
16)----------------------DataSourceExec: partitions=1, partition_sizes=[1]
```
I guess we incorrectly consider them as "unmatched columns", even if the
filter matched, we still generate `CASE WHEN __scalar_sq_1.__always_true IS
NULL` condition. Ideally, we should avoid this.
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