indexes

# File activerecord/lib/active_record/connection_adapters/mysql/schema_statements.rb, line 8
        def indexes(table_name)
          indexes = []
          current_index = nil
          execute_and_free("SHOW KEYS FROM #{quote_table_name(table_name)}", "SCHEMA") do |result|
            each_hash(result) do |row|
              if current_index != row[:Key_name]
                next if row[:Key_name] == "PRIMARY" # skip the primary key
                current_index = row[:Key_name]

                mysql_index_type = row[:Index_type].downcase.to_sym
                case mysql_index_type
                when :fulltext, :spatial
                  index_type = mysql_index_type
                when :btree, :hash
                  index_using = mysql_index_type
                end

                indexes << [
                  row[:Table],
                  row[:Key_name],
                  row[:Non_unique].to_i == 0,
                  [],
                  lengths: {},
                  orders: {},
                  type: index_type,
                  using: index_using,
                  comment: row[:Index_comment].presence
                ]
              end

              if row[:Expression]
                expression = row[:Expression]
                expression = +"(#{expression})" unless expression.start_with?("(")
                indexes.last[-2] << expression
                indexes.last[-1][:expressions] ||= {}
                indexes.last[-1][:expressions][expression] = expression
                indexes.last[-1][:orders][expression] = :desc if row[:Collation] == "D"
              else
                indexes.last[-2] << row[:Column_name]
                indexes.last[-1][:lengths][row[:Column_name]] = row[:Sub_part].to_i if row[:Sub_part]
                indexes.last[-1][:orders][row[:Column_name]] = :desc if row[:Collation] == "D"
              end
            end
          end

          indexes.map do |index|
            options = index.last

            if expressions = options.delete(:expressions)
              orders = options.delete(:orders)
              lengths = options.delete(:lengths)

              columns = index[-2].map { |name|
                [ name.to_sym, expressions[name] || +quote_column_name(name) ]
              }.to_h

              index[-2] = add_options_for_index_columns(
                columns, order: orders, length: lengths
              ).values.join(", ")
            end

            IndexDefinition.new(*index)
          end
        end