Difference between N'String' vs U'String' literals in Oracle

Question

What is the meaning and difference between these queries?

SELECT U\'String\' FROM dual;

and

SELECT N\'String\' FROM dual;
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Answer 1

• N'string' just returns the string as NCHAR type.

• U'string' returns also NCHAR type, however it does additional processing to the string: it replaces \\ with \ and \xxxx with Unicode code point U+xxxx, where xxxx are 4 hexadecimal digits. This is similar to UNISTR('string'), the difference is that the latter returns NVARCHAR2.

U' literals are useful when you want to have a Unicode string independent from encoding and NLS settings.

Example:

select n'\€', u'\\\20ac', n'\\\20ac' from dual;

N'\€' U'\\\20AC' N'\\\20AC'
----- ---------- ----------
\€    \€         \\\20ac