[r2004-07-03 12:03:25 by beppe] Added box on queries

Original author: beppe
Date: 2004-07-03 12:03:25+00:00

web/manual/expressions.xml

@@ -660,4 +660,31 @@ the use of references:
 
 </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>