sequel alter table

require 'sequel'

DB = Sequel.connect('your_database_url')

# Step 1: Define the migration
Sequel.migration do
  change do
    # Step 2: Alter the table
    alter_table(:your_table) do
      # Step 3: Add a new column
      add_column :new_column, Integer

      # Step 4: Set a default value for the new column
      add_column :another_column, String, default: 'default_value'

      # Step 5: Modify the type and add a constraint to an existing column
      set_column_type :existing_column, String
      add_index :existing_column, unique: true

      # Step 6: Drop a column
      drop_column :obsolete_column

# Step 7: Run the migration[:schema_info].insert(migrator: 'your_migration_name'))