MySQL Cookbook

Sorting ENUM Values

Problem

ENUM values don’t sort like other string columns.

Solution

Learn how they work, and exploit those properties to your own advantage.

Discussion

ENUM is considered a string column type, but ENUM values have the special property that they are stored numerically with values ordered the same way they are listed in the table definition. These numeric values affect how enumerations are sorted, which can be very useful. Suppose you have a table named weekday containing an enumeration column day that has weekday names as its members:

CREATE TABLE weekday
(
    day ENUM('Sunday','Monday','Tuesday','Wednesday',
                'Thursday','Friday','Saturday')
);

Internally, MySQL defines the enumeration values Sunday through Saturday to have numeric values from 1 to 7. To see this for yourself, create the table using the definition just shown, then insert into it a record for each day of the week. However, to make the insertion order differ from sorted order (so you can see the effect of sorting), add the days in random order:

mysql> INSERT INTO weekday (day) VALUES('Monday'),('Friday'),
    -> ('Tuesday'), ('Sunday'), ('Thursday'), ('Saturday'), ('Wednesday');

Then select the values, both as strings and as the internal numeric value (the latter are obtained by using +0 to effect a string-to-number conversion):

mysql> SELECT day, day+0 FROM weekday; +-----------+-------+ | day | day+0 | +-----------+-------+ | Monday | 2 | | Friday | 6 | | Tuesday | 3 | | Sunday | 1 | | Thursday | 5 | | Saturday ...