code: def downgrade():
      """Unapply Increase maximum length of pool name in ``task_instance`` table to ``256`` characters"""
      conn = op.get_bind()
      if conn.dialect.name == "mssql":
          with op.batch_alter_table("task_instance") as batch_op:
              batch_op.drop_index("ti_pool")
              batch_op.alter_column(
                  "pool", type_=sa.String(50), nullable=False
              )
              batch_op.create_index("ti_pool", ["pool"])
      else:
          with op.batch_alter_table("task_instance") as batch_op:
              batch_op.alter_column(
                  "pool", type_=sa.String(50), nullable=False
              )
  
imports: from __future__ import annotations
  import sqlalchemy
  from alembic import op
label_desc: Use image node_id 2 for calling a global function with example usage: downgrade() without return types