[development] D6 SAPI: using hook_install to ALTER {tables}

[Moshe Weitzman]

>> Q3) Is it considered best practice to create your own tables rather  
>> than adding fields to existing tables "belonging" to other modules?
>
> definitely!  the other module might alter the schema and your data  
> could be destroyed.
>
> for example, sometimes, the best way to add a new (computed) column  
> is to create a new table with the schema you need, populate it with  
> fancy SELECT logic, and then drop the old one[1].  if your contrib  
> has hidden its own columns in the original table, the author of the  
> schema update won't know about your columns and will blindly drop  
> all your data after safely migrating their own columns to the new  
> table.
>
> -derek (dww)

i'll agree with dww that this is best practice for Contrib. But for a  
custom site, I think hook_schema_alter() is a terrific way to add  
columns to tables owned by other modules. this avoids joins, which can  
be very useful for improving performance. many core objects now use  
drupal_write_record() to write their data to the database and that  
function is designed to work with altered tables like this. In other  
words, core is deliberately moving towards allowing custom fields  
attached to "foreign" tables. We do need to some conventions for safe  
update functions so we avoid a scenario like dww describes.
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