mysql SQL_CALC_FOUND_ROWS

mysql> select SQL_CALC_FOUND_ROWS id from stu limit 0,5;
+----+
| id |
+----+
|  1 |
|  2 |
|  3 |
|  4 |
|  5 |
+----+
5 rows in set

mysql> select FOUND_ROWS();
+--------------+
| FOUND_ROWS() |
+--------------+
|         1006 |
+--------------+
1 row in set

SQL_CALC_FOUND_ROWS是一个标志, FOUND_ROWS() 后面是一个方法