Phantoms
Remember that the discussion so far is based on an
outrageous assumption: no inserts or deletes.
Suppose we have these transactions:
| T1 |
T2 |
select sum(salary)
from employee
where dept = 'sales' |
|
|
insert into employee(... 100000.00 ... 'sales') |
|
commit |
select sum(salary)
from employee
where dept = 'sales' |
|
|