How I can use variable as field name in plpgsql

Question

It is possible to make something like this in Postgres?

DECLARE variable VARCHAR  
BEGIN  
    variable := TG_RELNAME || '_id';  
    OLD.variable = 123;  
END;

I can't use value of variable as field_name...

ps my version of db is 8.4.

Answer 1

据我所知，唯一的方法就是进行一个额外的查询，例如

execute 'update ' || TG_RELNAME || ' set ' || variable ||' = 123';