Oracle PL/SQL Programming, 5th Edition

Tips for Iterative Processing

Loops are very powerful and useful constructs, but they are structures that you should use with care. Performance issues within a program often are traced back to loops, and any problem within a loop is magnified by its repeated execution. The logic determining when to stop a loop can be very complex. This section offers some tips on how to write loops that are clean, easy to understand, and easy to maintain.

Use Understandable Names for Loop Indexes

Software programmers should not have to make Sherlock Holmes-like deductions about the meaning of the start and end range values of the innermost FOR loops in order to understand their purpose. Use names that self-document the purposes of variables and loops. That way, other people will understand your code, and you will remember what your own code does when you review it three months later.

How would you like to try to understand—much less maintain—code that looks like this?

FOR i IN start_id .. end_id
LOOP
   FOR j IN 1 .. 7
   LOOP
      FOR k IN 1 .. 24
      LOOP
         build_schedule (i, j, k);
      END LOOP;
   END LOOP;
END LOOP;

It is hard to imagine that someone would write code based on such generic integer variable names (right out of Algebra 101), yet it happens all the time. The habits we pick up in our earliest days of programming have an incredible half-life. Unless you are constantly vigilant, you will find yourself writing the most abominable code. In the case above, the solution is simple—use variable names for the loop indexes ...