NULL Values
The NULL value means ``no data'' and 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.
NULL may be represented by \N when using the text file import
or export formats (LOAD DATA INFILE, SELECT ... INTO OUTFILE).
See section 6.4.9 LOAD DATA INFILE Syntax.