Add a few more xrefs, where they seemed appropriate: for example, refer

to the discussion of planner statistics in the documentation for the
default_statistics_target GUC var.

doc/src/sgml/ref/alter_table.sgml

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@@ -114,7 +114,10 @@ ALTER TABLE <replaceable class="PARAMETER">name</replaceable>
       sets the per-column statistics-gathering target for subsequent
       <xref linkend="sql-analyze" endterm="sql-analyze-title"> operations.
       The target can be set in the range 0 to 1000; alternatively, set it
-      to -1 to revert to using the system default statistics target.
+      to -1 to revert to using the system default statistics
+      target. For more information on the use of statistics by the
+      <productname>PostgreSQL</productname> query planner, refer to
+      <xref linkend="planner-stats">.
      </para>
     </listitem>
    </varlistentry>

doc/src/sgml/ref/create_table.sgml

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 -->
 
@@ -151,7 +151,10 @@ and <replaceable class="PARAMETER">table_constraint</replaceable> is:
     <term><replaceable class="PARAMETER">data_type</replaceable></term>
     <listitem>
      <para>
-      The data type of the column. This may include array specifiers.
+      The data type of the column. This may include array
+      specifiers. For more information on the data types included with
+      <productname>PostgreSQL</productname>, refer to <xref
+      linkend="datatype">.
      </para>
     </listitem>
    </varlistentry>

doc/src/sgml/runtime.sgml

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 -->
 
 <Chapter Id="runtime">
@@ -1562,11 +1562,13 @@ SET ENABLE_SEQSCAN TO OFF;
       <term><varname>default_statistics_target</varname> (<type>integer</type>)</term>
       <listitem>
        <para>
-        Sets the default statistics target for table columns that have not
-        had a column-specific target set via <command>ALTER TABLE SET
-        STATISTICS</>.  Larger values increase the time needed to do
-        <command>ANALYZE</>, but may improve the quality of the planner's
-        estimates. The default is 10.
+        Sets the default statistics target for table columns that have
+        not had a column-specific target set via <command>ALTER TABLE
+        SET STATISTICS</>.  Larger values increase the time needed to
+        do <command>ANALYZE</>, but may improve the quality of the
+        planner's estimates. The default is 10. For more information
+        on the use of statistics by the <productname>PostgreSQL</>
+        query planner, refer to <xref linkend="planner-stats">.
        </para>
       </listitem>
      </varlistentry>