Revert automatic set of sequence start to 1

The :class:`.Sequence` construct restores itself to the DDL behavior it
had prior to the 1.4 series, where creating a :class:`.Sequence` with
no additional arguments will emit a simple ``CREATE SEQUENCE`` instruction
**without** any additional parameters for "start value".   For most backends,
this is how things worked previously in any case; **however**, for
MS SQL Server, the default value on this database is
``-2**63``; to prevent this generally impractical default
from taking effect on SQL Server, the :paramref:`.Sequence.start` parameter
should be provided.   As usage of :class:`.Sequence` is unusual
for SQL Server which for many years has standardized on ``IDENTITY``,
it is hoped that this change has minimal impact.

Fixes: #7211
Change-Id: I1207ea10c8cb1528a1519a0fb3581d9621c27b31

1 files changed, 8 insertions, 0 deletions

diff --git a/lib/sqlalchemy/dialects/mssql/provision.py b/lib/sqlalchemy/dialects/mssql/provision.py
index f307c7140..a7ecf4aa3 100644
--- a/lib/sqlalchemy/dialects/mssql/provision.py
+++ b/lib/sqlalchemy/dialects/mssql/provision.py
@@ -14,6 +14,7 @@ from ...testing.provision import drop_all_schema_objects_pre_tables
 from ...testing.provision import drop_db
 from ...testing.provision import get_temp_table_name
 from ...testing.provision import log
+from ...testing.provision import normalize_sequence
 from ...testing.provision import run_reap_dbs
 from ...testing.provision import temp_table_keyword_args
 
@@ -116,3 +117,10 @@ def drop_all_schema_objects_pre_tables(cfg, eng):
                             )
                         )
                     )
+
+
+@normalize_sequence.for_db("mssql")
+def normalize_sequence(cfg, sequence):
+    if sequence.start is None:
+        sequence.start = 1
+    return sequence