How to drop all schemas in PostgreSQL with SQL query?

Question

I need to drop all the schemas in my database except public, information_schema and those LIKE 'pg_%'.

Here's what I've found: (this variant doesn't seem to work)

   CREATE OR REPLACE FUNCTION drop_all () 
   RETURNS VOID  AS
   $$
   DECLARE rec RECORD; 
   BEGIN
       -- Get all the schemas
        FOR rec IN
        SELECT DISTINCT schemaname
         FROM pg_catalog.pg_tables
         -- You can exclude the schema which you don't want to drop by adding another condition here
         WHERE schemaname NOT LIKE 'pg_%' AND schemaname != 'public' 
         AND schemaname != 'information_schema'
           LOOP
             EXECUTE 'DROP SCHEMA ' || rec.schemaname || ' CASCADE'; 
           END LOOP; 
           RETURN; 
   END;
   $$ LANGUAGE plpgsql;

   SELECT drop_all();

Another variant: (this one probably works but still crashes my app)

SELECT string_agg(format('DROP SCHEMA %I CASCADE;', nspname), E'\n')
FROM   pg_namespace WHERE nspname != 'public'
AND nspname NOT LIKE 'pg_%'
AND nspname != 'information_schema';

So, I wanted to make sure that the queries are correct or, hopefully, find another variant of the query.

Could anybody help me with finding another query for doing that?

Answer 1

It drops only schema with any table, because you are using the query:

 SELECT DISTINCT schemaname
         FROM pg_catalog.pg_tables

so schemas without any table are not dropped.

You have to use a different query

SELECT n.nspname AS "Name",
  pg_catalog.pg_get_userbyid(n.nspowner) AS "Owner"
FROM pg_catalog.pg_namespace n
WHERE n.nspname !~ '^pg_' AND n.nspname <> 'information_schema'