DROP COLUMN

Forking from http://drupal.org/node/109104

1. According to the notes (~ line 1187) in system.install, postgres supports dropping columns only from 7.4 (which is the minimum requirement for D6, but not for D5 and earlier).
2. The above, however, does not appear to be true. The provided link also states that additional steps might be required to "finish the job". To quote:
   

   The DROP COLUMN command does not physically remove the column, but simply makes it invisible to SQL operations. Subsequent inserts and updates of the table will store a NULL for the column. Thus, dropping a column is quick but it will not immediately reduce the on-disk size of your table, as the space occupied by the dropped column is not reclaimed. The space will be reclaimed over time as existing rows are updated. To reclaim the space at once, do a dummy UPDATE of all rows and then vacuum, as in:

   UPDATE table SET col = col;
   VACUUM FULL table;

3. There are a few places (early) in system.install where equivalent updates for pgSQL are avoided altogether stating point 1.
4. Testing on pgSQL 8.2.3, both the following syntaxes are supported:
   • ALTER TABLE {boxes} DROP COLUMN title
   • ALTER TABLE {boxes} DROP title

   The latter is what is used almost everywhere in system.install and according to the docs, is the recommended syntax. The keyword COLUMN is also considered to be needless noise. update_1006 uses the former.

A pgSQL-head should probably investigate this issue and establish a degree of consistency throughout system.install.

Thanks,
-K