How to check if row exists? about sqlpp11 HOT 18 CLOSED

if (db(select(count(t.alpha)).from(t).where(true)).front().count > 0) 
{ /* do something */ }

if (db(select(exists(select(t.alpha).from(t).where(true)))).front().exists) 
{ /* do something */ }

if ( db(select(t).count(t.nickname).where(t.nickname="Bob")) )
{ /* do something */ }

auto query = select(count(t.id)).from(t).where(t.nickname == "Bob");

auto result = db(query);

if (result.front().count > 0)
{ /* do something */ }

if (db(select(count(t.id)).from(t).where(t.nickname == "Bob")).front().count > 0) 
{ /* do something */ }

if (!db.select(t.id).from(t).where(t.nickname=="Bob").empty()))
{}

for (db(select(t.id).from(t).where(nickname == "Bob")))
{
   return true;
}
return false;

const bool exists = db(sqlpp::select(sqlpp::count(users_tbl.nickname)).from(users_tbl).where(users_tbl.nickname=nickname)).front().count > 0;

db_controller.cpp: In member function ‘bool support_server::db_controller::user_exists(const string&)’:
db_controller.cpp:111:131: error: no match for call to ‘(sqlpp::sqlite3::connection) (sqlpp::no_where_t<true>::_base_t<sqlpp::detail::statement_policies_t<void, sqlpp::no_with_t, sqlpp::select_t, sqlpp::no_select_flag_list_t, sqlpp::select_column_list_t<void, sqlpp::count_t<sqlpp::noop, sqlpp::column_t<support_server::users::users, support_server::users::users_::nickname> > >, sqlpp::from_t<void, support_server::users::users>, sqlpp::no_extra_tables_t, sqlpp::no_where_t<true>, sqlpp::no_group_by_t, sqlpp::no_having_t, sqlpp::no_order_by_t, sqlpp::no_limit_t, sqlpp::no_offset_t, sqlpp::no_union_t> >::_new_statement_t<std::integral_constant<bool, false>, sqlpp::where_t<void, sqlpp::assignment_t<sqlpp::column_t<support_server::users::users, support_server::users::users_::nickname>, sqlpp::text_operand> > >)’
   const bool exists = pimpl->db(sqlpp::select(sqlpp::count(users_tbl.nickname)).from(users_tbl).where(users_tbl.nickname=nickname)).front().count > 0;
                                                                                                                                   ^
In file included from db_controller.cpp:9:0:
/usr/local/include/sqlpp11/sqlite3/connection.h:88:9: note: candidate is:
   class connection: public sqlpp::connection
         ^
/usr/local/include/sqlpp11/sqlite3/connection.h:280:10: note: template<class T> decltype (t._run((*(sqlpp::sqlite3::connection*)this))) sqlpp::sqlite3::connection::operator()(const T&)
     auto operator()(const T& t) -> decltype(t._run(*this))
          ^
/usr/local/include/sqlpp11/sqlite3/connection.h:280:10: note:   template argument deduction/substitution failed:
/usr/local/include/sqlpp11/sqlite3/connection.h: In substitution of ‘template<class T> decltype (t._run((*(sqlpp::sqlite3::connection*)this))) sqlpp::sqlite3::connection::operator()(const T&) [with T = sqlpp::bad_statement]’:
db_controller.cpp:111:131:   required from here
/usr/local/include/sqlpp11/sqlite3/connection.h:280:10: error: ‘const struct sqlpp::bad_statement’ has no member named ‘_run’

... where(users_tbl.nickname=nickname)

... where(users_tbl.nickname==nickname)

if ( db(count(t).where(t.nickname=="Bob")) )
{}

if ( db(exists(t).where(t.nickname=="Bob")) )
{}

db_controller.cpp:112:53: error: ‘class sqlpp::sqlite3::bind_result_t’ has no member named ‘from’
  const bool exists = db.select(users_tbl.id).from(users_tbl).where(users_tbl.nickname == nickname).empty();

if (!db.select(t.id).from(t).where(t.nickname=="Bob")).empty())
{}

const bool exists = (db.select(users_tbl.id).from(users_tbl).where(users_tbl.nickname == nickname)).empty();

db_controller.cpp:112:54: error: ‘class sqlpp::sqlite3::bind_result_t’ has no member named ‘from’
  const bool exists = !(db.select(users_tbl.id).from(users_tbl).where(users_tbl.nickname == nickname)).empty();

if (!db(select(t.id).from(t).where(t.nickname=="Bob")).empty())
{}

db(sqlpp::insert_into(users_tbl).set(users_tbl.nickname=nickname));

/usr/local/include/sqlpp11/insert_value_list.h:434:7: error: static assertion failed: At least one required column is missing in set()
       static_assert(not std::is_same<_database_t, void>::value or detail::have_all_required_columns<lhs_t<Assignments>...>::value, "At least one required column is missing in set()");
       ^