Disallow system_versioning_asof in DML

create or replace table t1 (x int) with system versioning;

create or replace table t2 (y int);

insert into t1 values (1);

insert into t2 values (1);

set system_versioning_asof= '1970-01-01 00:00:00';

delete t1, t2 from t1 join t2 where t1.x = t2.y;

select * from t1;

select * from t2;

drop tables t1, t2;