3.6.8. Calculating Visits Per Day

The following example shows how you can use the bit group functions to calculate the number of days per month a user has visited a Web page.

CREATE TABLE t1 (year YEAR(4), month INT(2) UNSIGNED ZEROFILL,             day INT(2) UNSIGNED ZEROFILL);INSERT INTO t1 VALUES(2000,1,1),(2000,1,20),(2000,1,30),(2000,2,2),            (2000,2,23),(2000,2,23);

The example table contains year-month-day values representing visits by users to the page. To determine how many different days in each month these visits occur, use this query:

SELECT year,month,BIT_COUNT(BIT_OR(1<<day)) AS days FROM t1       GROUP BY year,month;

Which returns:

+------+-------+------+| year | month | days |+------+-------+------+| 2000 |    01 |    3 || 2000 |    02 |    2 |+------+-------+------+

The query calculates how many different days appear in the table for each year/month combination, with automatic removal of duplicate entries.