[ PostgreSQL Instance ] (サーバー / クラスター)
       │
       ├── [ Database A ] (独立したデータ空間)
       │      │
       │      ├── < Schema: public > (デフォルト)
       │      │      ├── Table: users
       │      │      └── Table: orders
       │      │
       │      └── < Schema: inventory > (論理的なグループ)
       │             ├── Table: products
       │             └── Table: stocks
       │
       └── [ Database B ]
              └── < Schema: public >
                     └── Table: logs

１．データベース一覧

/*List Databases*/
\l+

/*List Databases*/
SELECT 
    datname AS database_name,
    pg_get_userbyid(datdba) AS owner,
    pg_size_pretty(pg_database_size(datname)) AS size
FROM pg_database
WHERE datistemplate = false;

２．スキーマ一覧

/*List Schemas*/
\dn+

/*List Schemas*/
SELECT schema_name 
FROM information_schema.schemata
WHERE schema_name NOT IN ('information_schema', 'pg_catalog') 
  AND schema_name NOT LIKE 'pg_toast%'
  AND schema_name NOT LIKE 'pg_temp%';

３．テーブル一覧

/*List Tables*/
\d
\ds     -- sequence のみ
\dt+    -- table のみ

/*List Tables*/
SELECT table_schema, table_name
FROM information_schema.tables
WHERE table_type = 'BASE TABLE'
  AND table_schema NOT IN ('information_schema', 'pg_catalog')
ORDER BY table_schema, table_name;

/*Change default search schema*/
SHOW search_path;
SET search_path=public;

４．カラム一覧

/*List Columns*/
\d TABLE_NAME

/*List Columns*/
SELECT column_name, data_type, is_nullable, column_default
FROM information_schema.columns
WHERE table_name = 'TABLE_NAME'/*変更*/
ORDER BY ordinal_position;