The ALL keyword is a multiset operator. Multiset operators combine the results of two nested tables into a single nested table.
The ALL keyword instructs Oracle to return all elements in nested_table1 that are not in nested_table2. For example, if a particular element occurs m times in nested_table1 and n times in nested_table2, then the result will have (m-n) occurrences of the element if m > n and 0 occurrences if m<=n.
Note that ALL is the default condition and does not normally need to be explicitly specified.
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