how to create duplicate role of a user in postgres - postgresql

Question

I need a new user but it should be granted all those privileges that the other existing user/role has.
e.g.
User A has SELECT privileges on Table1
User A has EXECUTE privileges on Table2
...
If a new User B is created, I need the same privileges as,
User B has SELECT privileges on Table1
User B has EXECUTE privileges on Table2
...
Dont ask why :/
Actually User A has custom privileges on different tables, schemas, and functions; so its very tedious and lengthy process to manually grant permissions to the new user. Any help would be good.

Answer 1

Try something like:
GRANT A TO B;
It will grant all right of role A to B.
For details read this chapter of the manual.

Answer 2

First understand that roles and users are the same thing. In fact there isn't a thing called a user really, it's just a ROLE with a LOGIN option.
Second roles can be granted to other roles.
Third priviledges on roles can be inherited.
So assuming you have created your user a like:
CREATE ROLE A LOGIN;
GRANT SELECT ON table1 TO a;
GRANT EXECUTE ON FUNCTION xxx TO a;
You should be able to create a second role that mirrors the first role like:
CREATE ROLE b LOGIN;
GRANT a TO b;

Answer 3

I had to write the pgpsql code to loop through the privileges of User A and grant it to User B. It was done without any problem.
create or replace function update_user_privileges() returns text as
$$
declare
info record;
str text;
begin
/*Grant privileges to user B the same as with user A for a given table schema*/
str:='';
FOR info IN
select * from information_schema.table_privileges where table_schema='public' and grantee = 'A'
LOOP
/*append the tables' name, for which we are assigning privileges from user A to B*/
str:= str ||info.table_name || ',';
/*this is the main statement to grant any privilege*/
execute 'GRANT '|| info.privilege_type ||' on table public.'|| info.table_name || ' to B';
END LOOP;
return str;
end
$$ language 'plpgsql';
Usage: Copy/paste this code to crate this function and then do
select update_user_privileges();
**You have to adapt it for your table-schema and table-names. Hope it helps anyone

Answer 4

Here's a quick way to create grant statements for newuser, by copying all grants on db mydb to grantee myuser.
pg_dump mydb -s | egrep '^(GRANT|REVOKE).+TO "myuser"' | sed -E "s/\"myuser\"/\"newuser\"/g"
Note: The -s flag makes pg_dump execute quickly, because it's only dumping schema info.
Example output
GRANT SELECT,INSERT,UPDATE ON TABLE tabl1e TO "newuser";
GRANT SELECT,INSERT,DELETE,UPDATE ON TABLE table2 TO "newuser";
GRANT ALL ON PROCEDURE myprocedure(ids bigint[]) TO "newuser";
Simply run the output SQL grants or pipe them to psql and you're all set.

Answer 5

I used following method to create a new user same as an existing user using Ubuntu.
Get a full dump of existing database.
Use the following command to extract every line with the user you want to clone.
cat /path/to/db_dump_file | grep "existing_user_name" >> /path/to/extract.sql
Open extract.sql with a text editor and replace existing username with new username.
Remove unwanted queries (if any).
Now you have new SQL queries to create the new user.
This worked for me just fine. Hope this will help someone.