Don't reorder PrimaryKeyConstraint columns if explicit

Dialed back the "order the primary key columns per auto-increment"
described in :ref:`change_mysql_3216` a bit, so that if the
:class:`.PrimaryKeyConstraint` is explicitly defined, the order
of columns is maintained exactly, allowing control of this behavior
when necessary.

Change-Id: I9e7902c57a96c15968a6abf53e319acf15680da0
Fixes: #3726

2 files changed, 23 insertions, 0 deletions

diff --git a/doc/build/changelog/changelog_11.rst b/doc/build/changelog/changelog_11.rst
index abb97229d..44ae8c2bb 100644
--- a/doc/build/changelog/changelog_11.rst
+++ b/doc/build/changelog/changelog_11.rst
@@ -34,6 +34,16 @@
         cases than we expected, which hints that perhaps there are some
         unknown string-INSERT cases too.
 
+    .. change::
+        :tags: bug, mysql
+        :tickets: 3726
+
+        Dialed back the "order the primary key columns per auto-increment"
+        described in :ref:`change_mysql_3216` a bit, so that if the
+        :class:`.PrimaryKeyConstraint` is explicitly defined, the order
+        of columns is maintained exactly, allowing control of this behavior
+        when necessary.
+
 .. changelog::
     :version: 1.1.0b1
     :released: June 16, 2016
diff --git a/doc/build/changelog/migration_11.rst b/doc/build/changelog/migration_11.rst
index 9772213ef..4e54b97e1 100644
--- a/doc/build/changelog/migration_11.rst
+++ b/doc/build/changelog/migration_11.rst
@@ -2397,6 +2397,19 @@ of just stating the AUTO_INCREMENT column *first* within the primary key::
         PRIMARY KEY (y, x)
     )ENGINE=InnoDB
 
+To maintain explicit control of the ordering of primary key columns,
+use the :class:`.PrimaryKeyConstraint` construct explicitly (1.1.0b2)
+(along with a KEY for the autoincrement column as required by MySQL), e.g.::
+
+    t = Table(
+        'some_table', metadata,
+        Column('x', Integer, primary_key=True),
+        Column('y', Integer, primary_key=True, autoincrement=True),
+        PrimaryKeyConstraint('x', 'y'),
+        UniqueConstraint('y'),
+        mysql_engine='InnoDB'
+    )
+
 Along with the change :ref:`change_3216`, composite primary keys with
 or without auto increment are now easier to specify;
 :paramref:`.Column.autoincrement`