ACOS(X) returns the arc cosine of X. : ACOS « Math Numeric Functions « MySQL Tutorial

1. MySQL Tutorial
2. Math Numeric Functions
3. ACOS

mysql>
ACOS(X)returns NULL if X is not in the range -1 to 1.
mysql>
mysql> SELECT ACOS(1);
+---------+
| ACOS(1) |
+---------+
|       0 |
+---------+
1 row in set (0.00 sec)

mysql> SELECT ACOS(0);
+-----------------+
| ACOS(0)         |
+-----------------+
| 1.5707963267949 |
+-----------------+
1 row in set (0.00 sec)

mysql>