Postgres has extensions, and that’s awesome! Of course as the author of CREATE EXTENSION I’m a little biased… just remember that the ability to extend Postgres is way more than just this command. The whole database system has been design from the ground up to allow for extensibility. Parts of the design is to be found in the way you can register new objects at runtime: functions of course, and also data types, operators, index support structures such as operator classes and families, even index access methods!

Today’s article shows a query that you can use to list those tables in your schemas that are using a data type which is provided by an extension.

I came up with the following query, that scans through our pg_depend catalog to find the data types provided by installed extensions, and then scans through pg_depend again to find tables that have attributes depending on those data types.

with etypes as
  select classid::regclass,
    from pg_depend
         join pg_extension e
           on refclassid = 'pg_extension'::regclass
          and refobjid = e.oid
  where classid = 'pg_type'::regclass
 select etypes.extname,
        etypes.objid::regtype as type,
        n.nspname as schema,
        c.relname as table,
        attname as column

  from pg_depend
       join etypes
         on etypes.classid = pg_depend.refclassid
        and etypes.objid = pg_depend.refobjid
       join pg_class c on c.oid = pg_depend.objid
       join pg_namespace n on n.oid = c.relnamespace
       join pg_attribute attr
         on attr.attrelid = pg_depend.objid
        and attr.attnum = pg_depend.objsubid
 where pg_depend.classid = 'pg_class'::regclass;

Here, the result is quite simple:

 extname │   type    │ schema  │  table  │  column  
 ip4r    │ ipaddress │ tweet   │ visitor │ ipaddr
 ip4r    │ ip4r      │ geolite │ blocks  │ iprange
 hll     │ hll       │ tweet   │ uniques │ visitors
 hstore  │ hstore    │ moma    │ audit   │ after
 hstore  │ hstore    │ moma    │ audit   │ before
(5 rows)

The reason I’m working on that is to provide the readers of my book The Art of PostgreSQL with an easier way to restore the database used throughout the book. In a previous version of it, I tried to be smarter that I should and the result isn’t easy enough to use… I got feedback about that, so let’s try and improve things!