Setting a customized option in a stored procedure

问题

I'm trying to set a custom option in a stored procedure, but it is storing the variable name and not contents of the variable.

CREATE OR REPLACE FUNCTION set_user(_user_id bigint, is_local boolean default true) returns void AS $$
BEGIN
  SET my.user_id TO _user_id;
END;
$$ LANGUAGE PLPGSQL;

select set_user(1);
select current_setting('my.user_id');
 current_setting 
-----------------
 _user_id   
(1 row)

I expect current_setting to return 1, not the string value "_user_id".

回答1:

First solution

Syntax for SET is:

SET [ SESSION | LOCAL ] configuration_parameter { TO | = } { value |'value' | DEFAULT }

where value is the new value for a given configuration_parameter.

In order to assign a value stored in _user_id variable, you need to generate a dynamic command and then EXECUTE it.

This would be the way to do that:

CREATE OR REPLACE FUNCTION set_user(_user_id bigint, is_local boolean default true) 
RETURNS void 
LANGUAGE PLPGSQL
AS $$
BEGIN
  EXECUTE 'SET my.user_id TO ' || quote_nullable(_user_id);
END;
$$;

Attaching SQL Fiddle link for testing purposes.

Note:

• quote_nullable() function would return NULL if the input argument is null. It may not be necessary in your case.

---

Second solution

You could also achieve the same thing with set_config() function as @a_horse_with_no_name noted. Your function would then look like that:

CREATE OR REPLACE FUNCTION set_user(_user_id bigint, is_local boolean default true) 
RETURNS void 
LANGUAGE PLPGSQL
AS $$
BEGIN
  PERFORM set_config('my.user_id', _user_id::TEXT, false);
END;
$$;

Attaching SQL Fiddle link for testing purposes.

Note:

• You have to explicitly cast second argument to a varchar type
• PERFORM is used to evaluate an expression and discard the result since it's not needed
• You could use quote_nullable() function here as well

来源：https://stackoverflow.com/questions/36293621/setting-a-customized-option-in-a-stored-procedure