Dmitry Yemanov wrote:

>"
>
>>1. open cursor for "select * from a where a.t_val in (select t_val from
>>t)"
>>
>>
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>And perform a full fetch from the cursor into some temporary space.
>Generally, an open cursor doesn't mean it's materialized.
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>
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>>This has the downside that it can be very memory intensive.
>>
>>
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>Exactly. And this is a major downside.
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>
>

Not at all. It has the semantics as if it were implemented that way,
but nothing says that it does have to be implemented that way. Big, big
difference between semantics and an implementation imperative.