Query statements MUST return the ROWID to be updatable. For example:
select * from employee where salary > 2000
would not be updatable, whereas:
select employee.*, rowid from employee where salary > 2000
would be updatable.
To reduce this obvious nuisance, you can use the TOAD-specific EDIT statement. For example:
edit employee where salary > 2000
If the resultset should be editable but remains read-only, make sure the TOAD Options > Data Grids – Data tab, Default to Read-Only Queries checkbox is NOT enabled