Dandandan commented on issue #1082:
URL:
https://github.com/apache/arrow-datafusion/issues/1082#issuecomment-942696160
It looks like PostgreSQL has some explicit operator (`HashSetOp`) for these
kind of things:
```sql
> explain select * from demo intersect select * from demo;
HashSetOp Intersect (cost=0.00..30.40 rows=160 width=458)
-> Append (cost=0.00..28.00 rows=320 width=458)
-> Subquery Scan on "*SELECT* 1" (cost=0.00..13.20 rows=160
width=458)
-> Seq Scan on demo (cost=0.00..11.60 rows=160 width=454)
-> Subquery Scan on "*SELECT* 2" (cost=0.00..13.20 rows=160
width=458)
-> Seq Scan on demo demo_1 (cost=0.00..11.60 rows=160
width=454)
```
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