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<H2><A NAME="s12">12. Frequently Asked Questions (FAQ)</A> </H2>
<P>
<UL>
<LI><B>Q1:</B> How do I modify existing tables ?
<P><B>A1:</B> There are several ways:
<P>
<UL>
<LI>Do it manually with the 'edittable' operator.
<P>
</LI>
<LI>Simply append the new record(s) (table2) to the old table
(table1):
<BLOCKQUOTE><CODE>
<PRE>
tail +3 < table2 >> table1
</PRE>
</CODE></BLOCKQUOTE>
<P>
</LI>
<LI>On large, indexed tables you can apply the changes
to a smaller journalling table (edit buffer) and then use
the 'update' operator. See
section
<A HREF="NoSQL-5.html#sec-bigtables">Big tables</A> for more details
on this method.
<P>
</LI>
<LI>Use the old table header to build a valid new record, modify
the fields of the latter and write the modified table back to
disk:
<BLOCKQUOTE><CODE>
<PRE>
addrow < table |
compute 'Column1="value1"; Column2="value2"; ...' > table.tmp
mv table.tmp table
</PRE>
</CODE></BLOCKQUOTE>
<P>
</LI>
<LI>Use the 'row' operator
to select only those records that you want to retain:
<BLOCKQUOTE><CODE>
<PRE>
row 'selection expression' < table > table.tmp
mv table.tmp table
</PRE>
</CODE></BLOCKQUOTE>
<P>
</LI>
<LI>Use the 'update' operator. The two
tables are assumed to have the respective primary key fields
in their leftmost columns.</LI>
</UL>
<P>
</LI>
<LI><B>Q2:</B> Will NoSQL ever provide record-level locking and update
facilities ?
<P><B>A2:</B> This is currently 'not on the cards'. NoSQL assumes that
the tables are collections of variable-length records. Record-level
update requires fixed-length records. It can be implemented
by right-padding the records with blanks to 'make room' for
updates, but that is a bit of a kludge, IMHO. If you need such
facilities you should rather use
<A HREF="http://www.rdb.com">/rdb</A>, or resort to
a more usual SQL DBMS, either free or commercial. I prefer the
solution outlined in
section
<A HREF="NoSQL-5.html#sec-bigtables">Big tables</A>.
</LI>
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