Add support for "real" sequences in mssql

Added support for "CREATE SEQUENCE" and full :class:`.Sequence` support for
Microsoft SQL Server.  This removes the deprecated feature of using
:class:`.Sequence` objects to manipulate IDENTITY characteristics which
should now be performed using ``mssql_identity_start`` and
``mssql_identity_increment`` as documented at :ref:`mssql_identity`. The
change includes a new parameter :paramref:`.Sequence.data_type` to
accommodate SQL Server's choice of datatype, which for that backend
includes INTEGER and BIGINT.   The default starting value for SQL Server's
version of :class:`.Sequence` has been set at 1; this default is now
emitted within the CREATE SEQUENCE DDL for all backends.

Fixes: #4235
Fixes: #4633
Change-Id: I6aa55c441e8146c2f002e2e201a7f645e667b916

1 files changed, 6 insertions, 3 deletions

diff --git a/lib/sqlalchemy/sql/compiler.py b/lib/sqlalchemy/sql/compiler.py
index fc66ca517..4bd19e04b 100644
--- a/lib/sqlalchemy/sql/compiler.py
+++ b/lib/sqlalchemy/sql/compiler.py
@@ -3743,14 +3743,17 @@ class DDLCompiler(Compiled):
             drop.element, use_table=True
         )
 
-    def visit_create_sequence(self, create, **kw):
+    def visit_create_sequence(self, create, prefix=None, **kw):
         text = "CREATE SEQUENCE %s" % self.preparer.format_sequence(
             create.element
         )
+        if prefix:
+            text += prefix
         if create.element.increment is not None:
             text += " INCREMENT BY %d" % create.element.increment
-        if create.element.start is not None:
-            text += " START WITH %d" % create.element.start
+        if create.element.start is None:
+            create.element.start = self.dialect.default_sequence_base
+        text += " START WITH %d" % create.element.start
         if create.element.minvalue is not None:
             text += " MINVALUE %d" % create.element.minvalue
         if create.element.maxvalue is not None: