1 files changed, 49 insertions, 7 deletions
diff --git a/doc/src/sgml/ref/explain.sgml b/doc/src/sgml/ref/explain.sgml
index 7f57112570..cc73bcf7ff 100644
--- a/doc/src/sgml/ref/explain.sgml
+++ b/doc/src/sgml/ref/explain.sgml
@@ -1,6 +1,11 @@
+<!--
+$Header: /cvsroot/pgsql/doc/src/sgml/ref/explain.sgml,v 1.8 1999/07/22 15:09:12 thomas Exp $
+Postgres documentation
+-->
+
 <refentry id="SQL-EXPLAIN">
  <refmeta>
-  <refentrytitle>
+  <refentrytitle id="SQL-EXPLAIN-TITLE">
    EXPLAIN
   </refentrytitle>
   <refmiscinfo>SQL - Language Statements</refmiscinfo>
@@ -16,7 +21,7 @@
 
  <refsynopsisdiv>
   <refsynopsisdivinfo>
-   <date>1998-09-01</date>
+   <date>1999-07-20</date>
   </refsynopsisdivinfo>
   <synopsis>
 EXPLAIN [ VERBOSE ] <replaceable class="PARAMETER">query</replaceable>        
@@ -95,6 +100,7 @@ EXPLAIN
   <title>
    Description
   </title>
+
   <para>
    This command outputs details about the supplied query.
    The default output is the computed query cost. 
@@ -127,16 +133,54 @@ EXPLAIN
   <title>
    Usage
   </title>
+
+  <para>
+   To show a query plan for a simple query on a table with a single
+   <type>int4</type> column and 128 rows:
+
+   <programlisting>
+EXPLAIN SELECT * FROM foo;
+    <computeroutput>
+NOTICE:  QUERY PLAN:
+
+Seq Scan on foo  (cost=5.22 rows=128 width=4)
+
+EXPLAIN
+    </computeroutput>
+   </programlisting>
+  </para>
+
   <para>
-   To show a query plan for a simple query:
+   For the same table with an index to support an
+   <firstterm>equijoin</firstterm> condition on the query,
+   <command>EXPLAIN</command> will show a different plan:
 
    <programlisting>
-EXPLAIN select * from foo;
+EXPLAIN SELECT * FROM foo WHERE i = 4;
+    <computeroutput>
 NOTICE:  QUERY PLAN:
 
-Seq Scan on foo  (cost=0.00 rows=0 width=4)
+Index Scan using fi on foo  (cost=2.05 rows=1 width=4)
 
 EXPLAIN
+    </computeroutput>
+   </programlisting>
+  </para>
+
+  <para>
+   And finally, for the same table with an index to support an
+   <firstterm>equijoin</firstterm> condition on the query,
+   <command>EXPLAIN</command> will show the following for a query
+   using an aggregate function:
+
+   <programlisting>
+EXPLAIN SELECT sum(i) FROM foo WHERE i = 4;
+    <computeroutput>
+NOTICE:  QUERY PLAN:
+
+Aggregate  (cost=2.05 rows=1 width=4)
+  ->  Index Scan using fi on foo  (cost=2.05 rows=1 width=4)
+    </computeroutput>
    </programlisting>
   </para>
  </refsect1>
@@ -145,8 +189,6 @@ EXPLAIN
   <title>
    Compatibility
   </title>
-  <para>
-  </para>
 
   <refsect2 id="R2-SQL-EXPLAIN-4">
    <refsect2info>