lib/sequel/migration_builder.rb
def alter_tables(current_table_names, tables)
      each_table(current_table_names, tables) do |table_name, table, last_table|
        hsh = table.dup
        hsh[:columns] = hsh[:columns].map {|c| Schema::DbColumn.build_from_hash(c) }
        operations = Schema::AlterTableOperations.
          build(@db_tables[table_name], hsh, :immutable_columns => @immutable_columns)
        unless operations.empty?
          all_operations = if @separate_alter_table_statements
                             operations.map {|o| [o] }
                           else
                             [operations]
                           end

          all_operations.each_with_index do |o, i|
            alter_table_statement table_name, o
            add_blank_line unless last_table && i + 1 == all_operations.size
          end
        end
      end
    end
def alter_tables(current_table_names, tables)
      each_table(current_table_names, tables) do |table_name, table, last_table|
        hsh = table.dup
        hsh[:columns] = hsh[:columns].map {|c| Schema::DbColumn.build_from_hash(c) }
        operations = Schema::AlterTableOperations.
          build(@db_tables[table_name], hsh, :immutable_columns => @immutable_columns)
        unless operations.empty?
          all_operations = if @separate_alter_table_statements
                             operations.map {|o| [o] }
                           else
                             [operations]
                           end

          all_operations.each_with_index do |o, i|
            alter_table_statement table_name, o
            add_blank_line unless last_table && i + 1 == all_operations.size
          end
        end
      end
    end
Generates any alter table statements for current tables.