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<A HREF="sql.html">SQL Reference Contents</A>
<H2><A NAME="sect0" HREF="#toc0">NAME </A></H2>
create version - construct a version class
<H2><A NAME="sect1" HREF="#toc1">SYNOPSIS </A></H2>
<B>create version
</B> classname1 <B>from </B> classname2 [<B>[ </B>abstime<B>] </B>] <BR>
<H2><A NAME="sect2" HREF="#toc2">DESCRIPTION </A></H2>
<I>Currently, the
versioning facility is not working.</I> <P>
This command creates a version class
<I>classname1</I> which is related to its parent class, <I>classname2</I>. Initially,
<I>classname1</I> has the same contents as <I>classname2.</I> As updates to <I>classname1</I>
occur, however, the content of <I>classname1</I> diverges from <I>classname2.</I> On
the other hand, any updates to <I>classname2</I> show transparently through to
<I>classname1</I>, unless the instance in question has already been updated in
<I>classname1</I>.<I></I> <P>
If the optional <I>abstime</I> clause is specified, then the version
is constructed relative to a <B>snapshot</B> of <I>classname2</I> as of the time specified.
<P>
Postgres uses the query rewrite rule system to ensure that <I>classname1</I>
is differentially encoded relative to <I>classname2.</I> Moreover, <I>classname1</I>
is automatically constructed to have the same indexes as <I>classname2</I>. It
is legal to cascade versions arbitrarily, so a tree of versions can ultimately
result. The algorithms that control versions are explained in [ONG90].
<H2><A NAME="sect3" HREF="#toc3">EXAMPLE </A></H2>
-- <BR>
--create a version foobar from a snapshot of <BR>
--barfoo as of January
17, 1990 <BR>
-- <BR>
create version foobar from barfoo [ "Jan 17 1990" ] <BR>
<H2><A NAME="sect4" HREF="#toc4">SEE
ALSO </A></H2>
create <A HREF="view.l.html">view(l)</A>
, <A HREF="merge.l.html">merge(l)</A>
.
<H2><A NAME="sect5" HREF="#toc5">BUGS </A></H2>
Snapshots (i.e., the optional <I>abstime</I>
clause) are not implemented in Postgres. <P>
<HR><P>
<A NAME="toc"><B>Table of Contents</B></A><P>
<UL>
<LI><A NAME="toc0" HREF="#sect0">NAME</A></LI>
<LI><A NAME="toc1" HREF="#sect1">SYNOPSIS</A></LI>
<LI><A NAME="toc2" HREF="#sect2">DESCRIPTION</A></LI>
<LI><A NAME="toc3" HREF="#sect3">EXAMPLE</A></LI>
<LI><A NAME="toc4" HREF="#sect4">SEE ALSO</A></LI>
<LI><A NAME="toc5" HREF="#sect5">BUGS</A></LI>
</UL>
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