如何查询数据库、表空间、表的大小？

gaussdb=#  SELECT datname, pg_database_size(datname), pg_database_size(datname)/1024/1024/1024 as "dataSize_GB" FROM pg_database;
       datname       | pg_database_size |    dataSize_GB    
---------------------+------------------+-------------------
 template1           |         79208460 | .0737686268985271
 template0           |         79208460 | .0737686268985271
 postgres            |       1398554636 |  1.30250550433993
 mysql_compatible_db |         79208460 | .0737686268985271
(4 rows)

gaussdb=#  SELECT pg_size_pretty(pg_tablespace_size('pg_default'));
 pg_size_pretty 
----------------
 345 MB
(1 row)

gaussdb=#  SELECT pg_size_pretty(pg_relation_size('table_name'));
pg_size_pretty 
----------------
 0 bytes
(1 row)