3中方法，不论什么一个都行

方法一 ，查一个表

select pg_size_pretty(pg_relation_size('table_name'));

方法二 ，查出全部表并按大小排序

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，查出全部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