BIT_COUNT(numeric_value)
BIT_COUNT()函数返回激活位 numeric_value 的位数。 下面的例子说明了使用BIT_COUNT()函数返回激活位的数量的一系列数字：
mysql> SELECT
BIT_COUNT(2) AS TWO,
BIT_COUNT(4) AS FOUR,
BIT_COUNT(7) AS SEVEN
+-----+------+-------+
| TWO | FOUR | SEVEN |
+-----+------+-------+
| 1 | 1 | 3 |
+-----+------+-------+
1 row in set (0.00 sec)
