Major Description
Updating a row can make it disappear from the view:
create table X (X varchar primary key, Y varchar);
create view X1 as select * from X where Y = '1';
upsert into X1 values('1', '1');
// now the row with key '1' is visible through the view
upsert into X1 values('1', '2');
// row with key '1' is no longer visible
upsert into X1 values('2', '2');
// the new row never shows up in the view