3中方法，任何一个都行

方法一 ，查一个表

select pg_size_pretty(pg_relation_size('table_name'));

方法二 ，查出所有表并按大小排序

SELECT 
table_schema || '.' || table_name 
AS table_full_name,pg_size_pretty(pg_total_relation_size('"' ||table_schema || '"."' || table_name || '"')) AS size
FROM 
information_schema.tables
ORDER BY
    pg_total_relation_size('"' || table_schema || '"."' || table_name || '"')
DESC limit 20

方法三，查出所有表按大小排序并分离data与index

SELECT table_name,pg_size_pretty(table_size) AS table_size,pg_size_pretty(indexes_size) AS indexes_size,pg_size_pretty(total_size) AS total_size FROM ( SELECT table_name,pg_table_size(table_name) AS table_size,pg_indexes_size(table_name) AS indexes_size,pg_total_relation_size(table_name) AS total_size FROM ( SELECT ('"' || table_schema || '"."' || table_name || '"') AS table_name FROM information_schema.tables ) AS all_tables ORDER BY total_size DESC ) AS pretty_sizes