mysql 如何统计去重后的数量

mysql> select * from books;
+------+--------+------+
| name | author | jb   |
+------+--------+------+
| lkj  | NULL   | NULL |
| lkj  | NULL   | NULL |
| lkj  | NULL   | NULL |
+------+--------+------+
3 rows in set (0.00 sec)

mysql> select count(distinct(name)) from books;
+-----------------------+
| count(distinct(name)) |
+-----------------------+
|                     1 |
+-----------------------+
1 row in set (0.22 sec)