Re: ERROR: missing FROM-clause entry for table "new"

I'm trying to define a trigger function that looks for changes in table A (table the trigger for the function is on) and write a delta record into table B.  So if a record has a value of 100 in table A, and it is updated to 50, the function should write –50 in table B. I can get the trigger to work with static SQL statements but for the actual code, I need to use dynamic SQL because I need to alter the insert statement to B depending on what column in table A is altered.  I can get the correct SQL generated but when I execute the string inside the trigger function I get an error because it doesn't seem to be able to see the NEW table when it's run with EXECUTE. 

So, this works in the trigger function:

Insert into A (col1,col2,…colN)

Select new.col1,new.co2…new.colN)

This doesn't:

sql := 'Insert into A (col1,col2,…colN) ';

sql := sql || 'Select new.col1,new.co2…new.colN)';

Execute sql;

ERROR:  missing FROM-clause entry for table "new"

There is nothing wrong with the resulting code from sql because if I output the string and put it in as static SQL in my trigger it works.

How do I build the string within the trigger and execute it with a reference to NEW?

Thanks in advance for the help,

James