koa-static-query

    const query = require('./db/query');

    app.use(static(path.join(process.cwd(),'public')));

    app.use(bodyparser());  //ctx.request.body

    app.use(router.routes());

    app.use(router.allowedMethods());

    let create_time = new Date();

    # search (vague) : 

    await query(`select *  from userlist where username like '%${key}%'`) 

    #     select : 

    await query('select * from userlist where username=?' ,[username])

    #     add ：

    await query(insert into userlist (username,...)  values (?,...),[username,...])

    #     delete : 

    await query('delete from userlist where id=?',[id])

    #     update ：

    await query('update userlist set username=?,.....  where username=?',[username,...])