Mod Authors: Please read if you are creating install.sql files

Applies to all versions.

Please do not do this:

SET @configuration_group_id=0;
SELECT @configuration_group_id:=configuration_group_id
FROM configuration_group
WHERE configuration_group_title= 'My Mod Name'
LIMIT 1;
DELETE FROM configuration WHERE configuration_group_id = @configuration_group_id;
DELETE FROM configuration_group WHERE configuration_group_id = @configuration_group_id;

If the mod has never been installed before, there is no such configuration group, so you wind up deleting configuration group 0.

This produces the problem described in this thread:
http://www.zen-cart.com/forum/showthread.php?t=170483

To avoid this, just have a separate "uninstall.sql" file and don't include the cleanup statements in your install.sql file.

You can tell that configuration group 0 has been deleted by looking at a product with a text field in your catalog product info page. You'll see something like this:

instead of something like this:

A better way to structure your SQL if you want to clean up before you add config entries (provided by @Numinix):

SELECT @configuration_group_id:=configuration_group_id
FROM configuration_group
WHERE configuration_group_title= 'YOUR-FEATURE-NAME'
LIMIT 1;
DELETE FROM configuration WHERE configuration_group_id = @configuration_group_id AND configuration_group_id != 0;
DELETE FROM configuration_group WHERE configuration_group_id = @configuration_group_id AND configuration_group_id != 0;

Please also do not blindly insert values into the configuration table, or any table for that matter. Always specify the column names.

Good example:

INSERT INTO configuration (configuration_id, configuration_title, configuration_key, configuration_value, configuration_description, configuration_group_id, sort_order, date_added, use_function, set_function) VALUES (NULL, 'Version', 'CSFB_VERSION', '1.0.0', 'Version installed:', " . $configuration_group_id . ", 0, NOW(), NULL, NULL);

Bad Example:

INSERT INTO configuration VALUES (NULL, 'Version', 'CSFB_VERSION', '1.0.0', 'Version  installed:', " . $configuration_group_id . ", 0, NOW(), NULL, NULL);

This is still a requirement, and I'm still seeing mods that come in that haven't done this. Please be sure to double check your mod!