Restrictions on Collection-Type Conversions

Because each collection data type (SET, MULTISET, and LIST) has different characteristics, conversions between collections with different collection types are disallowed. For example, elements stored in a LIST collection have a specific order associated with them. This order would be lost if the elements inserted into a LIST collection could be inserted into a MULTISET collection. Consequently, you cannot insert or update elements from one collection with elements from a different collection type even though the two collections might share the same element type. The following INSERT statement returns an error because the column on which the insert is performed is a MULTISET collection and the value being inserted is a LIST collection:

INSERT INTO m_set_tab SELECT col4 FROM list_tab -- returns error