wangyum commented on pull request #30222:
URL: https://github.com/apache/spark/pull/30222#issuecomment-721474620
Hive optimized it to `predicate: CASE WHEN ((a = 100)) THEN (false) WHEN ((b
> 1000)) THEN (true) WHEN (c is not null) THEN (false) ELSE (null) END (type:
boolean)`. But this condition can not push down. We can optimized it to `b >
1000` and push down it.
```
hive> explain SELECT *
> FROM (SELECT CASE
> WHEN a = 100 THEN 1
> WHEN b > 1000 THEN 2
> WHEN c IS NOT NULL THEN 3
> END AS x
> FROM t) tmp
> WHERE x = 2;
OK
STAGE DEPENDENCIES:
Stage-0 is a root stage
STAGE PLANS:
Stage: Stage-0
Fetch Operator
limit: -1
Processor Tree:
TableScan
alias: t
Statistics: Num rows: 1 Data size: 0 Basic stats: PARTIAL Column
stats: NONE
Filter Operator
predicate: CASE WHEN ((a = 100)) THEN (false) WHEN ((b > 1000))
THEN (true) WHEN (c is not null) THEN (false) ELSE (null) END (type: boolean)
Statistics: Num rows: 1 Data size: 0 Basic stats: PARTIAL Column
stats: NONE
Select Operator
expressions: CASE WHEN ((a = 100)) THEN (1) WHEN ((b > 1000))
THEN (2) WHEN (c is not null) THEN (3) ELSE (null) END (type: int)
outputColumnNames: _col0
Statistics: Num rows: 1 Data size: 0 Basic stats: PARTIAL
Column stats: NONE
ListSink
```
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