How to dynamically call a column in plpgsql

Hi!

I am trying to fetch a value from a column, where the
columnname is a value in another column.

See below ..

table constraint_1 (
...
cons_col VARCHAR(15) NOT NULL,
...
)


Then in the trigger (written in plpgsql) I want to
fetch the appropriate column from the NEW record.
--- trigger --
bla bla bla...

select cons_col from constraint_1 where bla = bla ...
-- the_val := NEW.cons_col;

bla. bla .bla.
return NEW;
bla bla bla..
----

Well I have tried a couple different things .. none
seem to work. I know that this is possible if the
trigger is written in C .. but it might be nice to
know how to do this in plpgsql.
Anyone out there that knows how to do this?



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