DRDS 支持一个位函数，即 BIT_COUNT()，其返回参数对应的二进制数中1的个数；若参数为NULL，则返回NULL。

1. mysql> SELECT BIT_COUNT(29), BIT_COUNT(b'101010');
2. +--------------+----------------------+
3. | BIT_COUNT(29) | BIT_COUNT(b'101010') |
4. +--------------+----------------------+
5. | 4 | 3 |
6. +--------------+----------------------+
7. 1 row in set (0.00 sec)
8. 
   
9. mysql> SELECT BIT_COUNT(NULL);
10. +-----------------+
11. | BIT_COUNT(NULL) |
12. +-----------------+
13. | NULL |
14. +-----------------+
15. 1 row in set (0.00 sec)