Oracle multiset, collection and records

Can anybody explain to me why records are required? Can't we just perform the same operation in PL/SQL using loop. Also when can a multiset recor开发者_如何学Cd query can be used? i.e. in which type of situation and which one would be the preference?

Here is a great link on this topic: http://www.oracle.com/technology/oramag/oracle/03-sep/o53plsql.html

Read the part about "Set Theory and Multiset Union".

It more or less works like UNION ALL, with one important difference:

"Unlike the SQL UNION set operator, the collection MULTISET UNION operator does not reorder the elements in the resulting collection. MULTISET UNION preserves the order in each collection and simply appends the contents of the second after the first. ".