NULLs

NULL means "no data".

NULL is case-insensitive. \N is a synonym for NULL and is case-sensitive. Note that a NULL is different from the number 0 or the empty string ''.

When you use the ORDER BY clause to sort data, NULLs come before other values in ascending order and after other values in descending order.

You can use \N to represent NULL in the LOAD DATA and SELECT ... INTO OUTFILE statements.

Here is an example:

obclient [test]> SELECT 1, NULL, \N FROM dual;

The return result is as follows:

+------+------+------+
| 1    | NULL | NULL |
+------+------+------+
|    1 | NULL | NULL |
+------+------+------+
1 row in set