help about dynamical sql

Hi,all:
  In my project:I have to use dynamical sql to create a trigger, suppose in one of my tests of dynamical sql,date information is like this:

   c_columnname='courses_score';
   :new.courses_score=10;
   fathertable=scores;
   f_columnname=score;

Then when executing dynamically the following statement

    select DESCRIPTIONl into variables_pkg.myinfo from '|| fathertable||'where '|| f_columnname||'=:new.'||c_columnname||'; we will get

    select DESCRIPTIONl into variables_pkg.myinfo from scores where score=:new.courses_score; But if I want to get the following statement:

    select DESCRIPTIONl into variables_pkg.myinfo from scores where score=10;

Then how to construct the dynamical sql? Any idea?
Thank you in advance!
Best Regards

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