PI() returns the value of |D (pi). : PI « Math Numeric Functions « MySQL Tutorial

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

The default number of decimal places displayed is seven, but MySQL uses the full double-precision value internally.

mysql>
mysql> SELECT PI();
+----------+
| PI()     |
+----------+
| 3.141593 |
+----------+
1 row in set (0.00 sec)

mysql> SELECT PI()+0.000000000000000000;
+---------------------------+
| PI()+0.000000000000000000 |
+---------------------------+
|      3.141592653589793100 |
+---------------------------+
1 row in set (0.00 sec)

mysql>