Quiz and question banks

I just tried it and it seems to work. Here is what I did:

1. I deleted the mdl_quesion_sojunit table.
2. I deleted the qtype_sojunit_version row from the mdl_config table.
3. I copied the code attached to your email into question/type/sojunit.
4. I went to the admin screen - the question type was re-installed.
   
5. I checked in the database to see that the table had actually been created - it had.

Remember that you have to consider the install and upgrade cases separately. Here is roughly what happens when the upgrade code checks to see if anything needs to be upgraded. (The code that does this is in function upgrade_plugins in lib/adminlib.php, you can look at that to see all the details.)

For each plugin of this type (e.g. myqtype) {

 Check that question/type/myqtype/version.php, .../db/upgrade.php and .../db/install.php exist.

 if ($CFG->qtype_myqtype_version exists, and is less than the number in version.php) {
 Call the upgrade function xmldb_qtype_myqtype_upgrade from
 upgrade.php, passing the old version number ($CFG->qtype_myqtype_version)
 which says what is currently installed
 Update $CFG->qtype_myqtype_version to the latest number from version.php
 to record what is currently installed
 }

 else if ($CFG->qtype_myqtype_version does not exist) {
 Create the tables from the definitions in install.xml
 Update $CFG->qtype_myqtype_version to the latest number from version.php
 to record what is currently installed
 }
}

So, to give a specific example of what you need to do as a plugin author. Suppose you make version 2008080100 of your plugin what has one table (say question_myqtype) with two columns, col1 and col2. Then you create version 2008080200 of your plugin which adds a third column, newcol to the table. The for those two releases, the files you need are:

2008080100 release

version.php contains $plugin->version=2008080100
db/install.xml contains the definition of a table question_myqtype with two columns col1 and col2.
There is no upgrade.php at this stage.

2008080200 release

version.php contains $plugin->version=2008080200
db/install.xml contains the definition of a table question_myqtype with three columns col1, col2 and newcol.
upgrade.php contains a single block of code inside the upgrade function, enclosed in an if ($oldversion < 2008080200) check, that adds the column newcol to the table question_myqtype.

In both these cases, install.xml should have been created with the XMLDB editor that you can find under Admin -> Experimental -> XMLDB. XMLDB editor can also generate the block of code in the upgrade file.

So, to put it another way, install.xml should always contain the most up-to-date table definitions and is only used for new installs. upgrade.php contains the code for upgrading from old installs to the latest version, and is only used for upgrading where a previous version of the plugin was installed.