1. It is useful to store UNICODE character or national character values with fixed length.
2. Max. size is 2000 chars/bytes.
3. You specify the national character set as either AL16UTF16 or UTF8 when you create your database.
AL16UTF16 and UTF8
1. AL16UTF16 and UTF8 are two encoding forms of the Unicode character set (UTF-16 and CESU-8, correspondingly) and hence NCHAR is a Unicode-only data type.
2. One code point has always 2 bytes in AL16UTF16 and from 1 to 3 bytes in UTF8, depending on the particular character encoded by the code point.
3. Oracle ensures that all values stored in an NCHAR column have the length of size characters.
4. If you insert a value that is shorter than the column length, then Oracle blank-pads the value to the column length.
5. If you try to insert a value that is too long for the column, then Oracle returns an error. Note that if the national character set is UTF8, blank-padding does not guarantee that all column values have the same byte length.
6. You can omit size from the column definition. The default value is 1.
7. The maximum value of size is 1000 characters when the national character set is AL16UTF16, and 2000 characters when the national character set is UTF8.
8. However, independently, the absolute maximum length of any character value that can be stored into an NCHAR column is 2000 bytes.
9. For example, even if you define the column length to be 1000 characters, Oracle returns an error if you try to insert a 1000-character value but the national character set is UTF8 and all code points are 3 bytes wide.
10. The value of size is a length constraint, not guaranteed capacity.
11. If you want an NCHAR column to be always able to store size characters in both national character sets, use a value of size that is less than or equal to 666.
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