Make the behavior of HAVING without GROUP BY conform to the SQL spec.

Formerly, if such a clause contained no aggregate functions we mistakenly
treated it as equivalent to WHERE.  Per spec it must cause the query to
be treated as a grouped query of a single group, the same as appearance
of aggregate functions would do.  Also, the HAVING filter must execute
after aggregate function computation even if it itself contains no
aggregate functions.

2 files changed, 16 insertions, 4 deletions

diff --git a/doc/src/sgml/query.sgml b/doc/src/sgml/query.sgml
index 366820e5546..e573db56cb6 100644
--- a/doc/src/sgml/query.sgml
+++ b/doc/src/sgml/query.sgml
@@ -1,5 +1,5 @@
 <!--
-$PostgreSQL: pgsql/doc/src/sgml/query.sgml,v 1.43 2005/01/22 22:56:36 momjian Exp $
+$PostgreSQL: pgsql/doc/src/sgml/query.sgml,v 1.44 2005/03/10 23:21:20 tgl Exp $
 -->
 
  <chapter id="tutorial-sql">
@@ -783,8 +783,9 @@ SELECT city, max(temp_lo)
     will be inputs to the aggregates.  On the other hand, the
     <literal>HAVING</literal> clause always contains aggregate functions.
     (Strictly speaking, you are allowed to write a <literal>HAVING</literal>
-    clause that doesn't use aggregates, but it's wasteful. The same condition
-    could be used more efficiently at the <literal>WHERE</literal> stage.)
+    clause that doesn't use aggregates, but it's seldom useful. The same
+    condition could be used more efficiently at the <literal>WHERE</literal>
+    stage.)
    </para>
 
    <para>
diff --git a/doc/src/sgml/ref/select.sgml b/doc/src/sgml/ref/select.sgml
index 855412c36c9..93218e16c2e 100644
--- a/doc/src/sgml/ref/select.sgml
+++ b/doc/src/sgml/ref/select.sgml
@@ -1,5 +1,5 @@
 <!--
-$PostgreSQL: pgsql/doc/src/sgml/ref/select.sgml,v 1.81 2005/01/22 23:22:19 momjian Exp $
+$PostgreSQL: pgsql/doc/src/sgml/ref/select.sgml,v 1.82 2005/03/10 23:21:20 tgl Exp $
 PostgreSQL documentation
 -->
 
@@ -452,6 +452,17 @@ HAVING <replaceable class="parameter">condition</replaceable>
     unambiguously reference a grouping column, unless the reference
     appears within an aggregate function.
    </para>
+    
+   <para>
+    The presence of <literal>HAVING</literal> turns a query into a grouped
+    query even if there is no <literal>GROUP BY</> clause.  This is the
+    same as what happens when the query contains aggregate functions but
+    no <literal>GROUP BY</> clause.  All the selected rows are considered to
+    form a single group, and the <command>SELECT</command> list and
+    <literal>HAVING</literal> clause can only reference table columns from
+    within aggregate functions.  Such a query will emit a single row if the
+    <literal>HAVING</literal> condition is true, zero rows if it is not true.
+   </para>
   </refsect2>
 
   <refsect2 id="sql-select-list">