Re: Optimizing nbtree ScalarArrayOp execution, allowing multi-column ordered scans, skip scan

There seems to be an assertion failure with this change in HEAD

TRAP: failed Assert("leftarg->sk_attno == rightarg->sk_attno"), File: "../../src/backend/access/nbtree/nbtutils.c", Line: 3246, PID: 1434532

It can be reproduced by: 

create table t(a int);
insert into t select 1 from generate_series(1,10);
create index on t (a desc);
set enable_seqscan = false;
select * from t where a IN (1,2) and a IN (1,2,3);

It's triggered when a scankey's strategy is set to invalid. While for a descending ordered column, 

the strategy needs to get fixed to its commute strategy. That doesn't work if the strategy is invalid.

Attached a demo fix.

Regards,

Donghang Lin

(ServiceNow)