Per-Group Descriptive Statistics

13.3.1 Problem

You want to produce descriptive statistics for each subgroup of a set of observations.

13.3.2 Solution

Use aggregate functions, but employ a GROUP BY clause to arrange observations into the appropriate groups.

13.3.3 Discussion

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. dev.'
 -> FROM testscore
 -> GROUP BY sex;
+-----+----+------+---------+---------+--------+-----------+
| sex | n | sum | minimum | maximum | mean | std. dev. |
+-----+----+------+---------+---------+--------+-----------+
| M | 10 | 71 | 4 | 9 | 7.1000 | 1.7000 |
| F | 10 | 75 | 4 | 10 | 7.5000 | 1.8574 |
+-----+----+------+---------+---------+--------+-----------+

By age and sex:

mysql> SELECT age, 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. dev.'
 -> FROM testscore
 -> GROUP BY age, sex;
+-----+-----+---+------+---------+---------+--------+-----------+
| age | sex | n | sum | minimum | maximum | mean | std. dev. |
+-----+-----+---+------+---------+---------+--------+-----------+
| 5 | M | 2 | 9 | 4 | 5 | 4.5000 | 0.5000 |
| 5 | F | 2 | 13 | 6 | 7 | 6.5000 | 0.5000 |
| 6 | M | 2 | 17 | 8 | 9 | 8.5000 | 0.5000 |
| 6 | F | 2 | 10 | 4 | 6 | 5.0000 | 1.0000 |
| 7 | M | 2 | 14 | 6 | 8 | 7.0000 | 1.0000 |
| 7 | F | 2 | 16 | 7 | 9 | 8.0000 | 1.0000 |
| 8 | M | 2 | 15 | 6 | 9 | 7.5000 | 1.5000 |
| 8 | F | 2 | 17 | 7 | 10 | 8.5000 | 1.5000 |
| 9 | M | 2 | 16 | 7 | 9 | 8.0000 | 1.0000 |
| 9 | F | 2 | 19 | 9 | 10 | 9.5000 | 0.5000 |
+-----+-----+---+------+---------+---------+--------+-----------+

Using the mysql Client Program

Writing MySQL-Based Programs

Record Selection Techniques

Working with Strings

Working with Dates and Times

Sorting Query Results

Generating Summaries

Modifying Tables with ALTER TABLE

Obtaining and Using Metadata

Importing and Exporting Data

Generating and Using Sequences

Using Multiple Tables

Statistical Techniques

Handling Duplicates

Performing Transactions

Introduction to MySQL on the Web

Incorporating Query Resultsinto Web Pages

Processing Web Input with MySQL

Using MySQL-Based Web Session Management

Appendix A. Obtaining MySQL Software

Appendix B. JSP and Tomcat Primer

Appendix C. References



MySQL Cookbook
MySQL Cookbook
ISBN: 059652708X
EAN: 2147483647
Year: 2005
Pages: 412
Authors: Paul DuBois

Similar book on Amazon

Flylib.com © 2008-2017.
If you may any questions please contact us: flylib@qtcs.net