Commit c16f9a88 authored by Pietro Abate's avatar Pietro Abate
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[r2004-07-03 12:03:25 by beppe] Added box on queries

Original author: beppe
Date: 2004-07-03 12:03:25+00:00
parent bce02df8
...@@ -660,4 +660,31 @@ the use of references: ...@@ -660,4 +660,31 @@ the use of references:
</box> </box>
<box title="Queries" link="sel">
<p>
CDuce is endowed with a <code>select_from_where</code> syntax to perform some SQL-like queries. The general form of select expressions is
</p>
<sample><![CDATA[
select %%e%% from
%%p1%% in %%e1%%
%%p2%% in %%e2%%
:
%%pn%% in %%en%%
where %%b%%
]]></sample>
<p>
where <code>%%e%%</code> is an expression <code>%%b%%</code> a boolean
expression, the <code>%%pi%%</code>'s are patterns, and the
<code>%%ei%%</code>'s are sequence expressions.
</p>
<p>
A <code>select</code> expression works like a set of nested
<code>transform</code> expressions. The advantage of using selections is that
these queries are automatically optimized by applying classical logic SQL query
optimizations techniques (automatic optimization can be disabled).
</p>
</box>
</page> </page>
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