SIGN

SIGN(X)

Devuelve el signo del argumento como -1, 0 ó 1, dependiendo de si X es negativo, cero o positivo:

mysql> SELECT SIGN(-32);
+-----------+
| SIGN(-32) |
+-----------+
|        -1 |
+-----------+
1 row in set (0.00 sec)

mysql> SELECT SIGN(0);
+---------+
| SIGN(0) |
+---------+
|       0 |
+---------+
1 row in set (0.00 sec)

mysql> SELECT SIGN(234);
+-----------+
| SIGN(234) |
+-----------+
|         1 |
+-----------+
1 row in set (0.00 sec)