| From: | Alpha Beta <dzjitaru(at)gmail(dot)com> |
|---|---|
| To: | pgsql-general(at)postgresql(dot)org |
| Subject: | subset of attributes |
| Date: | 2011-02-15 22:01:28 |
| Message-ID: | AANLkTimh+S5r6g_A2MMXQeMp3LXX4GdT49QMhjfqe=xA@mail.gmail.com |
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| Lists: | pgsql-general |
Hi,
while reading about databases, I didn't understand what can be subset of
attributes, see the following :
Let Ri (Xi) be a relation sheme, where Xi is a set of attributes. and if t
is a tuple for Ri (Xi) and Y is a subset of Xi, then t[Y] denote the
subtuple of t corresponding to Y.
does a subset of attributes just means the instances that exist in each
tuple?
Best,
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