10-9. Counting the Members in a Collection
Problem
You have a collection, and you need to determine the total number of elements in the collection.
Solution
Invoke the built-in COUNT method on the collection. For example, the following code creates two collections: a varying array and an INDEX BY array. The code then invokes the COUNT method on both collections, doing so before and after adding some records to each.
DECLARE
TYPE vtype IS VARRAY(3) OF DATE;
TYPE ctype IS TABLE OF DATE INDEX BY BINARY_INTEGER;
vdates vtype := vtype (sysdate);
cdates ctype;
BEGIN
DBMS_OUTPUT.PUT_LINE ('vdates size is: ' || vdates.COUNT);
DBMS_OUTPUT.PUT_LINE ('cdates size is: ' || cdates.COUNT);
FOR i IN 1..3 LOOP
cdates(i) := SYSDATE + 1;
END LOOP;
DBMS_OUTPUT.PUT_LINE ('cdates size is: ' || cdates.COUNT);
END;
Executing this block of code produces the following results:
vdates size is: 1
cdates size is: 0
cdates size is: 3
How It Works
The variable vdates is initialized with one value, so its size is reported as 1 even though it is defined to hold a maximum of three values. The variable cdates is not initialized, so it is first reported with a size of 0. The loop creates and sets three collection values, which increases its count to 3.
Assigning a value directly to cdates(i) is allowed because cdates is an INDEX BY collection. Assigning a value to vdates in the loop would cause an error because the array has only one defined value. See the EXTEND method later in this chapter for more information on assigning values to non-INDEX BY collections.
The COUNT method is especially useful when used on a collection populated with a fetch from BULK COLLECT statement to determine the number of records fetched or to process records in a FOR .. LOOP.