Table sizes

[luis.roberto@xxxxxxxxxxxxxxx]

Hi!

I'm trying to use this query to get table sizes, however I'm getting a strange error:

select tablename,pg_relation_size(tablename::text) 

  from pg_tables;

In PG 13:

SQL Error [42P01]: ERROR: relation "sql_implementation_info" does not exist

In PG 12:

SQL Error [42P01]: ERROR: relation "sql_parts" does not exist