October 2002
Intermediate to advanced
1024 pages
27h 26m
English
You want to produce descriptive statistics for each subgroup of a set of observations.
Use aggregate functions, but
employ a GROUP BY clause
to arrange observations into the appropriate groups.
The preceding section shows how to compute descriptive statistics for
the entire set of scores in the testscore table.
To be more specific, you can use GROUP
BY to divide the observations into groups and
calculate statistics for each of them. For example, the subjects in
the testscore table are listed by age and sex, so
it’s possible to calculate similar statistics by age
or sex (or both) by application of appropriate
GROUP BY clauses.
By age:
mysql>SELECT age, COUNT(score) AS n,->SUM(score) AS sum,->MIN(score) AS minimum,->MAX(score) AS maximum,->AVG(score) AS mean,->STD(score) AS 'std. dev.'->FROM testscore->GROUP BY age;+-----+---+------+---------+---------+--------+-----------+ | age | n | sum | minimum | maximum | mean | std. dev. | +-----+---+------+---------+---------+--------+-----------+ | 5 | 4 | 22 | 4 | 7 | 5.5000 | 1.1180 | | 6 | 4 | 27 | 4 | 9 | 6.7500 | 1.9203 | | 7 | 4 | 30 | 6 | 9 | 7.5000 | 1.1180 | | 8 | 4 | 32 | 6 | 10 | 8.0000 | 1.5811 | | 9 | 4 | 35 | 7 | 10 | 8.7500 | 1.0897 | +-----+---+------+---------+---------+--------+-----------+
By sex:
mysql>SELECT sex, COUNT(score) AS n,->SUM(score) AS sum,->MIN(score) AS minimum,->MAX(score) AS maximum,->AVG(score) AS mean,->STD(score) AS 'std. ...