CARDINALITY returns the number of elements in a nested table. The return type is NUMBER. If the nested table is empty, or is a null collection, then CARDINALITY returns NULL.
The following example shows the number of elements in the nested table column ad_textdocs_ntab of the sample table pm.print_media:
SELECT product_id, CARDINALITY(ad_textdocs_ntab) Cardinality
FROM print_media
ORDER BY product_id, cardinality;
PRODUCT_ID CARDINALITY
---------- -----------
2056 3
2268 3
3060 3
3106 3