A REPEAT UNTIL loop executes its body and then checks to see if the condition for stopping execution is TRUE. You can implement a REPEAT UNTIL loop with the simple loop as follows:
LOOP ... EXIT WHEN <condition>; END LOOP;
This loop does not execute even once. When you use the REVERSE keyword, the year_index moves from highest to lowest value (the reverse of the normal order). However, the low value of the range must still be first, as shown here:
FOR year_index IN REVERSE 1990 .. 1999 LOOP calc_sales (year_index); END LOOP;
At first glance, you might think that a FOR loop would make the most sense (“for each…”). A FOR loop would be a mistake in this context, however, because there is also a conditional exit (under certain conditions, stop after 12 years). You should use a FOR loop only when you are going to iterate unconditionally through every value between the low- and high-range limits. Instead, use a simple or WHILE loop to satisfy this requirement.
Since there is no conditional exit described in this requirement, you should use the cursor FOR loop.
Use the WHILE loop, since there are conditions under which you do not want the loop body to execute even a single time.
Do not use a generic loop index name (i); it makes the code less readable, and it looks unprofessional. In addition, the conditional EXIT from the FOR loop should be removed. Instead, use a FOR loop that iterates as follows:
FOR i IN 1 .. LEAST (76, total_count) LOOP ...