MySQL Manual
3 Tutorial Introduction
- 3.5 Examples of Common Queries
- 3.5.1 The Maximum Value for a Column
- 3.5.2 The Row Holding the Maximum of a Certain Column
- 3.5.3 Maximum of Column per Group
- 3.5.4 The Rows Holding the Group-wise Maximum of a Certain Field
- 3.5.5 Using user variables
- 3.5.6 Using Foreign Keys
- 3.5.7 Searching on Two Keys
- 3.5.8 Calculating Visits Per Day
- 3.5.9 Using
AUTO_INCREMENT
3.5.8 Calculating Visits Per Day
The following shows an idea of 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);
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 above calculates how many different days were used for a given year/month combination, with automatic removal of duplicate entries.
