### 3.6.8 計算每日訪問量 下面的示例展示了如何使用位組函數計算用戶每月訪問 Web 頁面的天數. ```sql CREATE TABLE t1 (year YEAR(4), month INT UNSIGNED, day INT UNSIGNED); INSERT INTO t1 VALUES(2000,1,1),(2000,1,20),(2000,1,30),(2000,2,2), (2000,2,23),(2000,2,23); ``` 示例表包含了用戶訪問頁面的年月日值, 要確定每個月都有那些天發生了訪問, 使用以下查詢: ```sql SELECT year,month,BIT_COUNT(BIT_OR(1<<day)) AS days FROM t1 GROUP BY year,month; ``` 返回結果為: ```sql +------+-------+------+ | year | month | days | +------+-------+------+ | 2000 | 1 | 3 | | 2000 | 2 | 2 | +------+-------+------+ ``` 查詢計算每個年月組合在表中出現的天數, 并自動刪除重復條目.