wangyum commented on pull request #30222:
URL: https://github.com/apache/spark/pull/30222#issuecomment-743725618
@cloud-fan @dongjoon-hyun We can improve the following case to reduce
`Union` operator:
```sql
create table t1 using parquet as select * from range(100);
create table t2 using parquet as select * from range(200);
create temp view v1 as
select 'a' as event_type, * from t1
union all
select CASE WHEN id = 1 THEN 'b' WHEN id = 3 THEN 'c' end as event_type, *
from t2;
explain select * from v1 where event_type = 'a';
== Physical Plan ==
Union
:- *(1) Project [a AS event_type#8, id#10L]
: +- *(1) ColumnarToRow
: +- FileScan parquet default.t1[id#10L] Batched: true, DataFilters: [],
Format: Parquet,
+- *(2) Project [CASE WHEN (id#11L = 1) THEN b WHEN (id#11L = 3) THEN c END
AS event_type#9, id#11L]
+- *(2) Filter (CASE WHEN (id#11L = 1) THEN b WHEN (id#11L = 3) THEN c
END = a)
+- *(2) ColumnarToRow
+- FileScan parquet default.t2[id#11L] Batched: true, DataFilters:
[(CASE WHEN (id#11L = 1) THEN b WHEN (id#11L = 3) THEN c END = a)], Format:
Parquet
explain select * from v1 where event_type = 'b';
== Physical Plan ==
*(1) Project [CASE WHEN (id#11L = 1) THEN b WHEN (id#11L = 3) THEN c END AS
event_type#8, id#11L AS id#10L]
+- *(1) Filter (CASE WHEN (id#11L = 1) THEN b WHEN (id#11L = 3) THEN c END =
b)
+- *(1) ColumnarToRow
+- FileScan parquet default.t2[id#11L] Batched: true, DataFilters:
[(CASE WHEN (id#11L = 1) THEN b WHEN (id#11L = 3) THEN c END = b)], Format:
Parquet
```
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