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Combining similar rows from a MySQL database select

If you're selecting data from a MySQL database and you want to report back the total or average for a column, you can use a function such as avg or sum on the column. If you want to choose only certain records to include in your sum or average, add a WHERE clause and if you want to produce a separate sum or average for each unique value in another column, use a GROUP BY clause.

Basic data:


mysql> select agid, asking from sales where agid > 9;
+------+--------+
| agid | asking |
+------+--------+
| 10 | 225000 |
| 10 | 195000 |
| 10 | 237500 |
| 11 | 465000 |
| 11 | 275000 |
+------+--------+


Summing all the asking prices:


mysql> select sum(asking) from sales where agid > 9;
+-------------+
| sum(asking) |
+-------------+
| 1397500 |
+-------------+


Summing the asking prices agid by agid:


mysql> select agid, sum(asking) from sales where agid > 9 group by agid;
+------+-------------+
| agid | sum(asking) |
+------+-------------+
| 10 | 657500 |
| 11 | 740000 |
+------+-------------+


See [url=http://www.wellho.net/mouth/515_MySQL-an-FAQ.html]our MySQL FAQ[/url] for other hints on MySQL SELECT commands.

(written 2006-01-17, updated 2006-06-09)

 
Associated topics are indexed as below, or enter http://melksh.am/nnnn for individual articles
S157 - More MySQL commands
  [158] MySQL - LEFT JOIN and RIGHT JOIN, INNER JOIN and OUTER JOIN - (2004-12-20)
  [159] MySQL - Optimising Selects - (2004-12-21)
  [279] Getting a list of unique values from a MySQL column - (2005-04-14)
  [449] Matching in MySQL - (2005-09-24)
  [494] MySQL - a score of things to remember - (2005-11-12)
  [502] SELECT in MySQL - choosing the rows you want - (2005-11-22)
  [513] MySQL - JOIN or WHERE to link tables correctly? - (2005-12-01)
  [515] MySQL - an FAQ - (2005-12-03)
  [517] An occasional chance, and reducing data to manageable levels - (2005-12-04)
  [572] Giving the researcher power over database analysis - (2006-01-22)
  [581] Saving a MySQL query results to your local disc for Excel - (2006-01-29)
  [591] Key facts - SQL and MySQL - (2006-02-04)
  [673] Helicopter views and tartans - (2006-04-06)
  [1213] MySQL - the order of clauses and the order of actions - (2007-06-01)
  [1235] Outputting numbers as words - MySQL with Perl or PHP - (2007-06-17)
  [1331] MySQL joins revisited - (2007-09-03)
  [1574] Joining MySQL tables revisited - finding nonmatching records, etc - (2008-03-15)
  [1735] Finding words and work boundaries (MySQL, Perl, PHP) - (2008-08-03)
  [1904] Ruby, Perl, Linux, MySQL - some training notes - (2008-11-23)
  [2110] MySQL - looking for records in one table that do NOT correspond to records in another table - (2009-03-31)
  [2259] Grouping rows for a summary report - MySQL and PHP - (2009-06-27)
  [2448] MySQL - efficiency and other topics - (2009-10-10)
  [2643] Relating tables with joins in MySQL - (2010-02-21)
  [2644] Counting rows in joined MySQL tables - (2010-02-22)
  [2645] Optimising and caching your MySQL enquiries - (2010-02-22)
  [2647] Removing duplicates from a MySQL table - (2010-02-22)
  [3061] Databases - why data is split into separate tables, and how to join them - (2010-11-20)
  [3270] SQL - Data v Metadata, and the various stages of data selection - (2011-04-29)
  [4481] Extracting data from backups to restore selected rows from MySQL tables - (2015-05-01)


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