postgres
diff --git a/‎doc/src/sgml/ref/create_table.sgml
Copy file name to clipboardExpand all lines: doc/src/sgml/ref/create_table.sgml
+15-7Lines changed: 15 additions & 7 deletions b/‎doc/src/sgml/ref/create_table.sgml
Copy file name to clipboardExpand all lines: doc/src/sgml/ref/create_table.sgml
+15-7Lines changed: 15 additions & 7 deletions
@@ -492,9 +492,11 @@ CREATE [ [ GLOBAL | LOCAL ] { TEMPORARY | TEMP } | UNLOGGED ] TABLE [ IF NOT EXI
      <para>
       The <literal>UNIQUE</literal> constraint specifies that a
       group of one or more columns of a table can contain
-      only unique values. The behavior of the unique table constraint
-      is the same as that for column constraints, with the additional
-      capability to span multiple columns.
+      only unique values. The behavior of a unique table constraint
+      is the same as that of a unique column constraint, with the
+      additional capability to span multiple columns.  The constraint
+      therefore enforces that any two rows must differ in at least one
+      of these columns.
      </para>
 
      <para>
@@ -503,10 +505,10 @@ CREATE [ [ GLOBAL | LOCAL ] { TEMPORARY | TEMP } | UNLOGGED ] TABLE [ IF NOT EXI
      </para>
 
      <para>
-      Each unique table constraint must name a set of columns that is
+      Each unique constraint should name a set of columns that is
       different from the set of columns named by any other unique or
-      primary key constraint defined for the table.  (Otherwise it
-      would just be the same constraint listed twice.)
+      primary key constraint defined for the table.  (Otherwise, redundant
+      unique constraints will be discarded.)
      </para>
     </listitem>
    </varlistentry>
@@ -531,11 +533,17 @@ CREATE [ [ GLOBAL | LOCAL ] { TEMPORARY | TEMP } | UNLOGGED ] TABLE [ IF NOT EXI
 
      <para>
       <literal>PRIMARY KEY</literal> enforces the same data constraints as
-      a combination of <literal>UNIQUE</> and <literal>NOT NULL</>, but
+      a combination of <literal>UNIQUE</> and <literal>NOT NULL</>.  However,
       identifying a set of columns as the primary key also provides metadata
       about the design of the schema, since a primary key implies that other
       tables can rely on this set of columns as a unique identifier for rows.
      </para>
+
+     <para>
+      Adding a <literal>PRIMARY KEY</literal> constraint will automatically
+      create a unique btree index on the column or group of columns used in the
+      constraint.
+     </para>
     </listitem>
    </varlistentry>