The update SQL file(s) are located in a directory that is listed in the manifest file:
<update> <schemas> <schemapath type="mysql">sql/updates</schemapath> </schemas> </update>
There is a file for each component version. Each file name must match the version string in the manifest file for that version. Joomla uses this string to determine which SQL files(s) to execute, and in what order they will be executed. Joomla uses the PHP version_compare function for this. Familiarize yourself with this command. Your version sequence needs to adhere to the conventions of this command. For example, the SQL files for version 3.1 include:
1.0.sql (empty) 1.1.sql UPDATE `#__democompupdate_mytable` SET myvalue='Version 1.1 text' WHERE id=1; 1.1.1.sql UPDATE `#__democompupdate_mytable` SET myvalue='Version 1.1.1 text' WHERE id=1; 1.2.sql INSERT INTO `#__democompupdate_mytable` (id,myvalue) VALUES (2,'Version 1.2 text'); 1.2.1.sql UPDATE `#__democompupdate_mytable` SET myvalue='Version 1.2.1 text' WHERE id=2; 1.3.sql INSERT INTO `#__democompupdate_mytable` (id,myvalue) VALUES (3,'Version 1.3 text');
This example has complete install files for component versions 1.0 (initial), 1.1.1 and 1.3. Update SQL files are included for additional incremental component versions (1.1, 1.2 and 1.2.1) between these three versions. These extra versions illustrate the process for updates that span more than one incremental version.
Joomla executes the database updates in the sequence that would occur, as if the user had updated each version separately. This would be necessary if an incremental database update depended on the correct update from the previous version. An example would be: an addition of a table value during one version depended on the insertion of a new table field during the update of the previous version.
Joomla uses the PHP function version_compare to define the execution order of the SQL files. The sequencing of your component version string must adhere to that defined by the version_compare function.