Using the TO Keyword to Define a Range

The TO keyword implies a range operator. The range is defined by left_expression and right_expression, and the STEP increment_expr option implicitly sets the number of increments. If you use the TO keyword, loop_var must be an INT or SMALLINT data type.

The next example shows two equivalent FOR statements. Each uses the TO keyword to define a range. The first uses the IN keyword, and the second uses an equal sign ( = ). Each statement causes the loop to execute five times: 
FOR index_var IN (12 TO 21 STEP 2)
   -- statement block
END FOR;

FOR index_var = 12 TO 21 STEP 2
   -- statement block
END FOR;

If you omit the STEP option, the database server gives increment_expr the value of -1 if right_expression is less than left_expression, or +1 if right_expression is more than left_expression. If increment_expr is specified, it must be negative if right_expression is less than left_expression, or positive if right expression is more than left_expression.

The two statements in the following example are equivalent. In the first statement, the STEP increment is explicit. In the second statement, the STEP increment is implicitly 1: 
FOR index IN (12 TO 21 STEP 1)
   -- statement block
END FOR;

FOR index = 12 TO 21
   -- statement block
END FOR;

The database server initializes the value of loop_var to the value of left_expression. In subsequent iterations, the server adds increment_expr to the value of loop_var and checks increment_expr to determine whether the value of loop_var is still between left_expression and right_expression. If so, the next iteration occurs. Otherwise, an exit from the loop takes place. Or, if you specify another range, the variable takes on the value of the first element in the next range.