ATAN(Y,X), ATAN2(Y,X) returns the arc tangent of the two variables X and Y. : ATAN « Math Numeric Functions « MySQL Tutorial

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

mysql>
mysql>
mysql> SELECT ATAN(-2,2);
+-------------------+
| ATAN(-2,2)        |
+-------------------+
| -0.78539816339745 |
+-------------------+
1 row in set (0.00 sec)

mysql> SELECT ATAN2(PI(),0);
+-----------------+
| ATAN2(PI(),0)   |
+-----------------+
| 1.5707963267949 |
+-----------------+
1 row in set (0.00 sec)

mysql>