[Plugin:wordpress simple survey] database query problem

Hello,

I have made changes to the wordpress simple survey plugin to add some question set besides the question.

Question set includes their questions and questions further contains its own set of answers.

$questions_set  = stripslashes_deep($wpdb->get_results("SELECT * FROM ".WPSS_QUESSET_DB." WHERE quiz_id='$quiz_id' ORDER BY id",ARRAY_A));
  $questions  = stripslashes_deep($wpdb->get_results("SELECT * FROM ".WPSS_QUESTIONS_DB." WHERE quiz_id='$quiz_id' ORDER BY rand() limit 1",ARRAY_A));

Question set table and question table is linked with an ID which is primary key of question set.
I want to execute only those questions which always equals the question_set_id.

I am new to wordpress database.

How to do that?