Example 11-1 Nesting a Query to Improve Performance

BEGIN
-- Inefficient, calls function for every row
   FOR item IN (SELECT DISTINCT(SQRT(department_id)) col_alias FROM employees)
   LOOP
      DBMS_OUTPUT.PUT_LINE(item.col_alias);
   END LOOP;
-- Efficient, only calls function once for each distinct value.
   FOR item IN
   ( SELECT SQRT(department_id) col_alias FROM
     ( SELECT DISTINCT department_id FROM employees)
   )
   LOOP
      DBMS_OUTPUT.PUT_LINE(item.col_alias);
   END LOOP;
END;
/