Manipulating Local Collections

Within PL/SQL, to manipulate the local collection, by using the  TABLE and CAST operators . The operands of CAST are a collection declared locally (in a PL/SQL unspecified block for illustration) and a SQL collection type. The CAST converts the local collection to the specified type. In that way, you can manipulate the collection as if it were a SQL database table. In the illustration below, you count the number of differences between a revised course list & the original (notice that the number of credits for the course 3720 changed from 4 to 3):


DECLARE
revised CourseList :=
CourseList(Course(1002, ’Expository Writing’, 3),
Course(2020, ’Film and Literature’, 4),
Course(2810, ’Discursive Writing’, 4),
Course(3010, ’Modern English Grammar ’, 3),
Course(3550, ’Realism and Naturalism’, 4),
Course(3720, ’Introduction to Shakespeare’,3),
Course(3760, ’Modern Drama’, 4),
Course(3822, ’The Short Story’, 4),
Course(3870, ’The American Novel’, 5),
Course(4210, ’20th-Century Poetry’, 4),
Course(4725, ’Advanced Workshop in Poetry’,5));
num_changed INTEGER;
BEGIN
SELECT COUNT(*) INTO num_changed
FROM TABLE(CAST(revised AS CourseList)) AS new,
TABLE(SELECT courses FROM department
WHERE name = ’English’) AS old
WHERE new.course_no = old.course_no AND
(new.title != old.title OR new.credits != old.credits);
DBMS_OUTPUT.PUT_LINE(num_changed);
END;