PostgreSQL 查詢所有數據庫大小，表大小，索引大小，以及表空間大小

1. 查詢數據庫大小

-- 查詢單個數據庫大小
select pg_size_pretty(pg_database_size('postgres')) as size;

-- 查詢所有數據庫大小
select datname, pg_size_pretty (pg_database_size(datname)) AS size from pg_database; 

2. 查詢表大小

-- 查詢單個表大小
select pg_size_pretty(pg_relation_size('mytab')) as size;

-- 查詢所有表大小
select relname, pg_size_pretty(pg_relation_size(relid)) as size from pg_stat_user_tables;

-- 查詢單個表的總大小，包括該表的索引大小
select pg_size_pretty(pg_total_relation_size('tab')) as size;

-- 查詢所有表的總大小，包括其索引大小
select relname, pg_size_pretty(pg_total_relation_size(relid)) as size from pg_stat_user_tables;

3. 查詢索引大小（暫時沒有一次性查詢所有索引大小的函數）

-- 查詢單個索引大小
select pg_size_pretty(pg_relation_size('myindex')) as size;

4. 查詢表空間大小

-- 查詢單個表空間大小
select pg_size_pretty(pg_tablespace_size('pg_default')) as size;

-- 查詢所有表空間大小
select spcname, pg_size_pretty(pg_tablespace_size(spcname)) as size from pg_tablespace;
-- 或
select spcname, pg_size_pretty(pg_tablespace_size(oid)) as size from pg_tablespace;