When you have to export the comments from the database you can use this short snippet to get the schema as markup.

content = ""
database_name = "DATABASE_NAME"
ActiveRecord::Base.connection.tables.each do |table_name|
  content << "h5. #{table_name}\n"
  rows = ActiveRecord::Base.connection.execute("SELECT table_comment 
    WHERE table_schema='#{database_name}' 
        AND table_name='#{table_name}';");
  puts rows.to_a.inspect
  content << rows.to_a.first.first << "\n"

  rows = ActiveRecord::Base.connection.execute("select table_name, column_name, DATA_TYPE, column_comment from INFORMATION_SCHEMA.COLUMNS where 1 AND TABLE_SCHEMA='#{database_name}' AND TABLE_NAME = '#{table_name}'")
  rows.each(:as => :hash) do |row| 
    puts row.inspect
    j = [ row["column_name"], row["DATA_TYPE"], row["column_comment"] ]

    content << "|#{j.join('|')}|\n"
end; ''
puts content

The output should be something like

Table name

table description

column name, type, description

….. the next table