How to get field value when field name is in variable

[parry2k]

I have one view with 3 fields like the view name is myview and it has following sql statement.

select fn,ln,city from tablea

I created a function like below:-

create function myfun(in t myview, in f varchar(50)) returns varchar(100) as

Now i want to pass row and name of field and let it return the value from function on basis of field name i pass to the function like

select myfun(*, 'fn') from myview

this suppose to return value of fn from myfun because i'm passing fn as a parameter name.

hope it is clear, if yes, how i can achieve this?

[rski]

You can use dynamic SQL. See here for EXECUTE command

http://www.postgresql.org/docs/current/static/plpgsql-statements.html

[parry2k]

No execute command didn't worked for me. this is what i did?

execute 't.' || quote_ident(f) into v;

in this case t and f are two parameters of function (as mentioned in question) and i declare v as a variable to get the value, it is not working

but if i do this

v := t.fn;

i get the value...so not sure how to get the value dynamically.

[rski]

where is select in that query

execute 't.' || quote_ident(f) into v;

Shouldn't there be somehting like that

execute 'select '||f||' from '|| t into v;

Or I do not understand your problem.

[parry2k]

Thanks for quick report but it is not a table where I can use select so it didn't worked. Even if I try

select fn into v from t

Without execute, it doesn't work. I think you didn't get my question.

[parry2k]

here is the link to an example and i'm trying to follow this

http://www.postgresql.org/docs/8.1/static/plpgsql-declarations.html

CREATE FUNCTION concat_selected_fields(in_t sometablename) RETURNS text AS $$
BEGIN
    RETURN in_t.f1 || in_t.f3 || in_t.f5 || in_t.f7;
END;
$$ LANGUAGE plpgsql;'

in my case , field name is dynamic