i found what is the needed privileges for the operation.
grant select on all_tab_columns to pl_sql_developer_role;
grant select on all_col_comments to pl_sql_developer_role;
grant select on ALL_OBJECTS to pl_sql_developer_role;
grant select on ALL_SYNONYMS to pl_sql_developer_role;
grant select...
in the sql window i'm try to see columns of
tables -
"select * from hearot t
where t."
and then i see the message -"ora-6550 ora-942 table or view does not exists"
i changed the "use DBA views if available"
on and off - it did not help.