PL/SQL - Nested Loops

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PL/SQL allows using one loop inside another loop. Following section shows a few examples to illustrate the concept.

The syntax for a nested basic LOOP statement in PL/SQL is as follows −

LOOP 
   Sequence of statements1 
   LOOP 
      Sequence of statements2 
   END LOOP; 
END LOOP;

The syntax for a nested FOR LOOP statement in PL/SQL is as follows −

FOR counter1 IN initial_value1 .. final_value1 LOOP 
   sequence_of_statements1 
   FOR counter2 IN initial_value2 .. final_value2 LOOP 
      sequence_of_statements2 
   END LOOP; 
END LOOP;

The syntax for a nested WHILE LOOP statement in Pascal is as follows −

WHILE condition1 LOOP 
   sequence_of_statements1 
   WHILE condition2 LOOP 
      sequence_of_statements2 
   END LOOP; 
END LOOP; 

Example

The following program uses a nested basic loop to find the prime numbers from 2 to 100 −

DECLARE 
   i number(3); 
   j number(3); 
BEGIN 
   i := 2; 
   LOOP 
      j:= 2; 
      LOOP 
         exit WHEN ((mod(i, j) = 0) or (j = i)); 
         j := j +1; 
      END LOOP; 
   IF (j = i ) THEN 
      dbms_output.put_line(i || ' is prime'); 
   END IF; 
   i := i + 1; 
   exit WHEN i = 50; 
   END LOOP; 
END; 
/

When the above code is executed at the SQL prompt, it produces the following result −

2 is prime 
3 is prime 
5 is prime 
7 is prime 
11 is prime 
13 is prime 
17 is prime 
19 is prime 
23 is prime 
29 is prime 
31 is prime 
37 is prime 
41 is prime 
43 is prime 
47 is prime  

PL/SQL procedure successfully completed.