MySQL 5.7 Release Notes
The NULL value means “no data.”
NULL can be written in any lettercase. A
synonym is \N (case-sensitive). Treatment of
\N as a synonym for NULL
in SQL statements is deprecated as of MySQL 5.7.18 and is
removed in MySQL 8.0; use NULL
instead.
Be aware that the NULL value is different
from values such as 0 for numeric types or
the empty string for string types. For more information, see
Section B.3.4.3, “Problems with NULL Values”.
For text file import or export operations performed with
LOAD DATA or
SELECT ... INTO
OUTFILE, NULL is represented by the
\N sequence. See Section 13.2.6, “LOAD DATA Statement”.
Use of \N in text files is unaffected by the
deprecation of \N in SQL statements.
For sorting with ORDER BY,
NULL values sort before other values for
ascending sorts, after other values for descending sorts.