code: def downgrade():
      conn = op.get_bind()
  
      op.create_table(
          "users",
          sa.Column("id", sa.Integer(), nullable=False),
          sa.Column("username", sa.String(length=250), nullable=True),
          sa.Column("email", sa.String(length=500), nullable=True),
          sa.Column("password", sa.String(255)),
          sa.Column("superuser", sa.Boolean(), default=False),
          sa.PrimaryKeyConstraint("id"),
          sa.UniqueConstraint("username"),
      )
  
      op.create_table(
          "chart",
          sa.Column("id", sa.Integer(), nullable=False),
          sa.Column("label", sa.String(length=200), nullable=True),
          sa.Column("conn_id", sa.String(length=250), nullable=False),
          sa.Column("user_id", sa.Integer(), nullable=True),
          sa.Column("chart_type", sa.String(length=100), nullable=True),
          sa.Column("sql_layout", sa.String(length=50), nullable=True),
          sa.Column("sql", sa.Text(), nullable=True),
          sa.Column("y_log_scale", sa.Boolean(), nullable=True),
          sa.Column("show_datatable", sa.Boolean(), nullable=True),
          sa.Column("show_sql", sa.Boolean(), nullable=True),
          sa.Column("height", sa.Integer(), nullable=True),
          sa.Column(
              "default_params", sa.String(length=5000), nullable=True
          ),
          sa.Column("x_is_date", sa.Boolean(), nullable=True),
          sa.Column("iteration_no", sa.Integer(), nullable=True),
          sa.Column("last_modified", sa.DateTime(), nullable=True),
          sa.ForeignKeyConstraint(
              ["user_id"],
              ["users.id"],
          ),
          sa.PrimaryKeyConstraint("id"),
      )
  
      if conn.dialect.name == "mysql":
          conn.execute(text("SET time_zone = '+00:00'"))
          op.alter_column(
              table_name="chart",
              column_name="last_modified",
              type_=mysql.TIMESTAMP(fsp=6),
          )
      else:
          if conn.dialect.name in ("sqlite", "mssql"):
              return
  
          if conn.dialect.name == "postgresql":
              conn.execute(text("set timezone=UTC"))
  
          op.alter_column(
              table_name="chart",
              column_name="last_modified",
              type_=sa.TIMESTAMP(timezone=True),
          )
  
imports: from __future__ import annotations
  import sqlalchemy
  from alembic import op
  from sqlalchemy import inspect, text
  from sqlalchemy.dialects import mysql
label_desc: Use image node_id 2 for calling a global function with example usage: downgrade() without return types