The NULL value means “no data.” NULL can be written in any lettercase. A synonym is \N (case sensitive).

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 12.2.6, “LOAD DATA INFILE Syntax”.

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.5.5.3, “Problems with NULL Values”.