The NULL value means “no data.”
NULL can be written in any lettercase.
Be aware that the NULL value is different
from values such as 0 for numeric types or
the empty string for string types. See
Section A.5.3, “Problems with NULL Values”.
For text file import or export operations performed with
LOAD DATA INFILE or SELECT ... INTO
OUTFILE, NULL is represented by the
\N sequence. See Section 13.2.5, “LOAD DATA INFILE Syntax”.
