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. 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 15.2.9, “LOAD DATA Statement”.

For sorting with ORDER BY, NULL values sort before other values for ascending sorts, after other values for descending sorts.