Do not support MSSQL less than v2017 in code

Our experimental support for MSSQL starts from v2017(in README.md) but
we still support 2000 & 2005 in code.
This PR removes this support, allowing us to use mssql.DATETIME2 in all
MSSQL DB.

airflow/migrations/db_types.py

@@ -29,31 +29,14 @@
 ######################################
 
 
-def _mssql_use_date_time2():
-    conn = context.get_bind()
-    result = conn.execute(
-        """SELECT CASE WHEN CONVERT(VARCHAR(128), SERVERPROPERTY ('productversion'))
-        like '8%' THEN '2000' WHEN CONVERT(VARCHAR(128), SERVERPROPERTY ('productversion'))
-        like '9%' THEN '2005' ELSE '2005Plus' END AS MajorVersion"""
-    ).fetchone()
-    mssql_version = result[0]
-    return mssql_version not in ("2000", "2005")
-
-
-MSSQL_USE_DATE_TIME2 = Proxy(_mssql_use_date_time2)
-
-
 def _mssql_TIMESTAMP():
     from sqlalchemy.dialects import mssql
 
-    if MSSQL_USE_DATE_TIME2:
-
-        class DATETIME2(mssql.DATETIME2):
-            def __init__(self, *args, precision=6, **kwargs):
-                super().__init__(*args, precision=precision, **kwargs)
+    class DATETIME2(mssql.DATETIME2):
+        def __init__(self, *args, precision=6, **kwargs):
+            super().__init__(*args, precision=precision, **kwargs)
 
-        return DATETIME2
-    return mssql.DATETIME
+    return DATETIME2
 
 
 def _mysql_TIMESTAMP():

airflow/migrations/db_types.pyi

@@ -24,5 +24,3 @@ TIMESTAMP = sa.TIMESTAMP
 
 StringID = sa.String
 """String column type with correct DB collation applied"""
-
-MSSQL_USE_DATE_TIME2: bool

airflow/migrations/versions/0088_2_2_0_improve_mssql_compatibility.py

@@ -30,7 +30,7 @@
 from alembic import op
 from sqlalchemy.dialects import mssql
 
-from airflow.migrations.db_types import MSSQL_USE_DATE_TIME2, TIMESTAMP
+from airflow.migrations.db_types import TIMESTAMP
 
 # revision identifiers, used by Alembic.
 revision = '83f031fd9f1c'
@@ -135,21 +135,12 @@ def recreate_mssql_ts_column(conn, op, table_name, column_name):
 
 def alter_mssql_datetime_column(conn, op, table_name, column_name, nullable):
     """Update the datetime column to datetime2(6)"""
-    if MSSQL_USE_DATE_TIME2:
-        op.alter_column(
-            table_name=table_name,
-            column_name=column_name,
-            type_=mssql.DATETIME2(precision=6),
-            nullable=nullable,
-        )
-
-
-def alter_mssql_datetime2_column(conn, op, table_name, column_name, nullable):
-    """Update the datetime2(6) column to datetime"""
-    if MSSQL_USE_DATE_TIME2:
-        op.alter_column(
-            table_name=table_name, column_name=column_name, type_=mssql.DATETIME, nullable=nullable
-        )
+    op.alter_column(
+        table_name=table_name,
+        column_name=column_name,
+        type_=mssql.DATETIME2(precision=6),
+        nullable=nullable,
+    )
 
 
 def upgrade():
@@ -199,7 +190,6 @@ def downgrade():
     conn = op.get_bind()
     if conn.dialect.name != 'mssql':
         return
-    alter_mssql_datetime2_column(conn, op, 'serialized_dag', 'last_updated', False)
     op.alter_column(table_name="xcom", column_name="timestamp", type_=TIMESTAMP, nullable=True)
     with op.batch_alter_table('task_reschedule') as task_reschedule_batch_op:
         task_reschedule_batch_op.alter_column(column_name='end_date', type_=TIMESTAMP, nullable=True)