// call function
  myQuery(1)
   .then((queryData)=>{
      console.log(queryData);
   })
   .catch((error)=>{
    console.log(error);
   });

  // query function
  myQuery(account_id){
    return new Promise( (resolve, reject) => {
      const sql = "SELECT * FROM user WHERE account_id = ?";
      this.db_connection.query(sql, [account_id], function(error, rows) {
        if (error)
        {
            const error = error.stack;
            reject(error);
        }
        if(rows.length === 0){
          reject('user is not exist');
        }else{ // user is exist
          resolve(rows);
        }
      });
    });
  }