sql - Oracle multiset, collection and records -

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Can anyone tell me why records are necessary? Can not we do the same thing while using Loop in PL / SQL? Also, when a multiset record query can be used? Which type of situation and which will be the priority?

Here's a great link on topic:

"Set theory and multiset Union ".

It performs less or less like a UNION ALL

with a very significant difference:

"SQL union set operator On the contrary, the collection Multistate Union operator rearranges the elements in the resulting archive.Multisette Union reserves order in each collection and simply adds the contents of the second after the first time. "


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