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NULL means a missing unknown value

The NULL value means "no data." NULL can be written in any lettercase. For operations performed with LOAD DATA INFILE or SELECT ... INTO OUTFILE, NULL is represented by the \N sequence. To test for NULL, you cannot use the arithmetic comparison operators such as =, . mysql> mysql> SELECT 1 = NULL, 1 <> NULL, 1 < NULL, 1 > NULL; +----------+-----------+----------+----------+ | 1 = NULL | 1 <> NULL | 1 < NULL | 1 > NULL | +----------+-----------+----------+----------+ |     NULL |      NULL |     NULL |     NULL | +----------+-----------+----------+----------+ 1 row in set (0.00 sec) mysql>