doc: Update catalog documentation for attstattarget nullable

Fixup for 4f62250.

Author: petere

doc/src/sgml/catalogs.sgml

@@ -1354,6 +1354,17 @@
       </para></entry>
      </row>
 
+     <row>
+      <entry role="catalog_table_entry"><para role="column_definition">
+       <structfield>attcollation</structfield> <type>oid</type>
+       (references <link linkend="catalog-pg-collation"><structname>pg_collation</structname></link>.<structfield>oid</structfield>)
+      </para>
+      <para>
+       The defined collation of the column, or zero if the column is
+       not of a collatable data type
+      </para></entry>
+     </row>
+
      <row>
       <entry role="catalog_table_entry"><para role="column_definition">
        <structfield>attstattarget</structfield> <type>int2</type>
@@ -1363,25 +1374,14 @@
        of statistics accumulated for this column by
        <link linkend="sql-analyze"><command>ANALYZE</command></link>.
        A zero value indicates that no statistics should be collected.
-       A negative value says to use the system default statistics target.
+       A null value says to use the system default statistics target.
        The exact meaning of positive values is data type-dependent.
        For scalar data types, <structfield>attstattarget</structfield>
        is both the target number of <quote>most common values</quote>
        to collect, and the target number of histogram bins to create.
       </para></entry>
      </row>
 
-     <row>
-      <entry role="catalog_table_entry"><para role="column_definition">
-       <structfield>attcollation</structfield> <type>oid</type>
-       (references <link linkend="catalog-pg-collation"><structname>pg_collation</structname></link>.<structfield>oid</structfield>)
-      </para>
-      <para>
-       The defined collation of the column, or zero if the column is
-       not of a collatable data type
-      </para></entry>
-     </row>
-
      <row>
       <entry role="catalog_table_entry"><para role="column_definition">
        <structfield>attacl</structfield> <type>aclitem[]</type>