MySQL Cookbook

Using a Join to Control Query Output Order

Problem

You want to sort a query’s output using a characteristic of the output that cannot be specified using ORDER BY. For example, you want to sort a set of rows by subgroups, putting first those groups with the most rows and last those groups with the fewest rows. But “number of rows in each group” is not a property of individual rows, so you can’t sort by it.

Solution

Derive the ordering information and store it in another table. Then join the original table to the derived table, using the derived table to control the sort order.

Discussion

Most of the time when you sort a query result, you use an ORDER BY (or GROUP BY) clause to name the column or columns to use for sorting. But sometimes the values you want to sort by aren’t present in the rows to be sorted. This is the case, for example, if you want to use group characteristics to order the rows. The following example uses the records in the driver_log table to illustrate this. The table looks like this:

mysql> SELECT * FROM driver_log ORDER BY id; +--------+-------+------------+-------+ | rec_id | name | trav_date | miles | +--------+-------+------------+-------+ | 1 | Ben | 2001-11-30 | 152 | | 2 | Suzi | 2001-11-29 | 391 | | 3 | Henry | 2001-11-29 | 300 | | 4 | Henry | 2001-11-27 | 96 | | 5 | Ben | 2001-11-29 | 131 | | 6 | Henry | 2001-11-26 | 115 | | 7 | Suzi | 2001-12-02 | 502 | | 8 | Henry | 2001-12-01 | 197 | | 9 | Ben | 2001-12-02 | 79 | | 10 | Henry | 2001-11-30 | 203 | +--------+-------+------------+-------+ ...