Question

如何在不使用子选择查询的情况下优化此查询？因为被告知不使用限制0,0。也是为了分页。

  select 
      e.logo,  e.id,  r.id,  r.userid, u.username,  u.fullname, e.push_notificaciones, e.nombre, r.reservationdate,  u.userphoto,  s.direccion, 
 r.comment, r.restcomment, r.status,  r.phonenumber, u.email, 
(select  u.fullname from users u where  parseID = r.approvalbyuserid) as approvalfullname, 
( select  u.userphoto from users u where  parseID = r.approvalbyuserid ) as approvaluserphoto 
    from 
      users u, 
      reservations r, 
      empresas e, 
      sucursales s 
    where 
      r.userid = 'AEnStpQk4B' 
      and e.id = r.restid 
      and u.parseID = r.userid 
      and s.id = r.sucursalid 
    limit 
      0, 
      20

Answer 1

您可以将其重写为

SELECT 
   e.logo,  e.id,  r.id,  r.userid, 
   u.username,  u.fullname, e.push_notificaciones, 
   e.nombre, r.reservationdate,  u.userphoto,  s.direccion, 
   r.comment, r.restcomment, r.status,  r.phonenumber, u.email, 
   a.fullname as approvalfullname, 
   a.userphoto as approvaluserphoto 
FROM reservations r
JOIN users u ON u.parseID = r.userid 
JOIN users a ON a.parseID = r.approvalbyuserid
JOIN empresas e ON e.id = r.restid 
JOIN sucursales s ON s.id = r.sucursalid 
WHERE 
   r.userid = 'AEnStpQk4B' 
LIMIT 0, 20

只要用户中的所有值都存在。如果没有，您可能需要LEFT JOIN

对于分页，LIMIT的第一个数字应为：

number_of_lines_per_page*(page_num -1)

每页20个项目，第3页：

LIMIT 20*(3-1), 20

但是，如果您希望获得没有任何限制的所有结果并在显示代码中处理，请跳过LIMIT行

没有这个子查询且没有限制偏移的Mysql优化

1 个答案: