How do I decide between using varrays and nested tables for modeling collections?
Varrays are useful when you need to maintain ordering of your collection elements. Varrays are very efficient when you always manipulate the entire collection as a unit, and that you don’t require querying on individual elements of the collections. Varrays are stored inline with the containing row if it is small and automatically stored as a LOBs by the system when its size is beyond a certain threshold. Nested tables are useful when there is no ordering among the collection elements and that efficient querying on individual elements are important. Elements of a collection type column are stored in a separate table, similar to parent-child tables in a relational schema.
