What is the difference between nvarchar and varchar in Oracle?

The main difference between nvarchar and varchar in Oracle database lies in the way they handle character data. Specifically:

1. varchar: stores variable-length character data. When storing data in a varchar column, space is allocated based on the actual length of the input characters, which may result in some space wastage. In a varchar column, each character occupies one byte of storage space.
2. nvarchar: stores Unicode character data, allowing for the storage of characters from multiple languages. When storing data, nvarchar columns use double byte storage for character data, which can result in larger storage space compared to varchar. nvarchar columns are typically used in situations where multiple languages need to be supported.

In general, if you need to store English character data, you can use varchar; if you need to store multi-language character data or support the Unicode character set, you can use nvarchar.