old_contents: #
  # Licensed to the Apache Software Foundation (ASF) under one
  # or more contributor license agreements.  See the NOTICE file
  # distributed with this work for additional information
  # regarding copyright ownership.  The ASF licenses this file
  # to you under the Apache License, Version 2.0 (the
  # "License"); you may not use this file except in compliance
  # with the License.  You may obtain a copy of the License at
  #
  #   http://www.apache.org/licenses/LICENSE-2.0
  #
  # Unless required by applicable law or agreed to in writing,
  # software distributed under the License is distributed on an
  # "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY
  # KIND, either express or implied.  See the License for the
  # specific language governing permissions and limitations
  # under the License.
  
  """Change default ``pool_slots`` to ``1``
  
  Revision ID: 8646922c8a04
  Revises: 449b4072c2da
  Create Date: 2021-02-23 23:19:22.409973
  
  """
  
  import sqlalchemy as sa
  from alembic import op
  
  # revision identifiers, used by Alembic.
  revision = '8646922c8a04'
  down_revision = '449b4072c2da'
  branch_labels = None
  depends_on = None
  airflow_version = '2.0.2'
  
  
  def upgrade():
      """Change default ``pool_slots`` to ``1`` and make pool_slots not nullable"""
      with op.batch_alter_table("task_instance", schema=None) as batch_op:
          batch_op.alter_column("pool_slots", existing_type=sa.Integer, nullable=False, server_default='1')
  
  
  def downgrade():
      """Unapply Change default ``pool_slots`` to ``1``"""
      with op.batch_alter_table("task_instance", schema=None) as batch_op:
          batch_op.alter_column("pool_slots", existing_type=sa.Integer, nullable=True, server_default=None)
  
new_contents: #
  # Licensed to the Apache Software Foundation (ASF) under one
  # or more contributor license agreements.  See the NOTICE file
  # distributed with this work for additional information
  # regarding copyright ownership.  The ASF licenses this file
  # to you under the Apache License, Version 2.0 (the
  # "License"); you may not use this file except in compliance
  # with the License.  You may obtain a copy of the License at
  #
  #   http://www.apache.org/licenses/LICENSE-2.0
  #
  # Unless required by applicable law or agreed to in writing,
  # software distributed under the License is distributed on an
  # "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY
  # KIND, either express or implied.  See the License for the
  # specific language governing permissions and limitations
  # under the License.
  
  """Change default ``pool_slots`` to ``1``
  
  Revision ID: 8646922c8a04
  Revises: 449b4072c2da
  Create Date: 2021-02-23 23:19:22.409973
  
  """
  
  import sqlalchemy as sa
  from alembic import op
  
  # revision identifiers, used by Alembic.
  revision = '8646922c8a04'
  down_revision = '449b4072c2da'
  branch_labels = None
  depends_on = None
  airflow_version = '2.0.2'
  
  
  def upgrade():
      """Change default ``pool_slots`` to ``1`` and make pool_slots not nullable"""
      op.execute("UPDATE task_instance SET pool_slots = 1 WHERE pool_slots IS NULL")
      with op.batch_alter_table("task_instance", schema=None) as batch_op:
          batch_op.alter_column("pool_slots", existing_type=sa.Integer, nullable=False, server_default='1')
  
  
  def downgrade():
      """Unapply Change default ``pool_slots`` to ``1``"""
      with op.batch_alter_table("task_instance", schema=None) as batch_op:
          batch_op.alter_column("pool_slots", existing_type=sa.Integer, nullable=True, server_default=None)
  
subject: Fix migration 0080_2_0_2 - Replace null values before setting column not null (#24585)