Not all valid view definitions are updatable. In other words, there are several types of view definitions that do not permit you to perform DELETE, INSERT, or UPDATE operations against them. The general rule for updatability of a view is that there must be a 1:1 correspondence between a row defined in a view and the same row defined in an underlying base table on which that view is defined. If that 1:1 correspondence does not exist, then the view is not updatable.
The following features, when specified as a component of a view definition, automatically make that view non‑updatable, or read‑only.
If a view definition specifies more than one table, it is not updatable.
You also cannot execute any of the following HELP statements against a non‑updatable view.