code: def add_column(conn, table, column_name, default_value=None, schema=None):
      
      activity_table = get_activity_table(schema=schema)
      data = {column_name: default_value}
      query = (
          activity_table
          .update()
          .values(
              old_data=sa.case(
                  [
                      (
                          sa.cast(activity_table.c.old_data, sa.Text) != '{}',
                          activity_table.c.old_data + data
                      ),
                  ],
                  else_=sa.cast({}, JSONB)
              ),
              changed_data=sa.case(
                  [
                      (
                          sa.and_(
                              sa.cast(
                                  activity_table.c.changed_data,
                                  sa.Text
                              ) != '{}',
                              activity_table.c.verb != 'update'
                          ),
                          activity_table.c.changed_data + data
                      )
                  ],
                  else_=activity_table.c.changed_data
              ),
          )
          .where(activity_table.c.table_name == table)
      )
      return conn.execute(query)
docs: Adds given column to `activity` table jsonb data columns.
  
      In the following example we reflect the changes made to our schema to
      activity table.
  
      ::
  
          import sqlalchemy as sa
          from alembic import op
          from postgresql_audit import add_column
  
  
          def upgrade():
              op.add_column('article', sa.Column('created_at', sa.DateTime()))
              add_column(op, 'article', 'created_at')
  
  
      :param conn:
          An object that is able to execute SQL (either SQLAlchemy Connection,
          Engine or Alembic Operations object)
      :param table:
          The table to remove the column from
      :param column_name:
          Name of the column to add
      :param default_value:
          The default value of the column
      :param schema:
          Optional name of schema to use.