NULL values

NULL indicates "no data".

NULL is case-insensitive. Its synonym is \N, which is case-sensitive. Note that a NULL value is different from the number 0 and the empty string ''.

When you use ORDER BY, NULL values appear before other values in ascending order and after other values in descending order.

LOAD DATA and SELECT ... INTO OUTFILE support using \N to represent NULL.

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