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3.6.9 Using AUTO_INCREMENT »
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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.


User Comments

Posted by [name withheld] on May 17 2005 2:39pm[Delete] [Edit]

It seems to me that it would be much simpler and intuitive to use something like this to query the days per month:

SELECT year, month, COUNT(DISTINCT day) AS days FROM t1 GROUP BY year,month;

Posted by Anders Henke on December 19 2005 1:55pm[Delete] [Edit]

Note that this example is not suitable for large-scale processing of weblogs ... it's missing indexes and usually one might use an aggregated counter if aggregated values are goal of the statistics.

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