如何重写这个复杂的 SQL 查询以不使用 MySQL 视图的子查询？答案

【问题标题】：How can I rewrite this complex SQL query to not use a subquery for MySQL Views?如何重写这个复杂的 SQL 查询以不使用 MySQL 视图的子查询？
【发布时间】：2009-10-13 18:05:27
【问题描述】：

无论出于何种原因，MySQL 都不支持视图中的子查询。在可预见的未来，我坚持使用 MySQL，我需要编写一个视图来将来自 EAV 样式表的数据聚合成更易读的格式。视图本身将充当基于 Ruby on Rails 的应用程序的模型（它是只读的，因此我可以安全地使用视图）。

如果我可以的话，我怎么能重写这个野兽来创建一个视图呢？我想如果必须的话，我可以创建一系列迷你视图，然后创建一个主视图（一个视图来统治它们，视情况而定），但我想知道还有另一种方法。

这是怪物；大量外连接是因为所有字段都是可选的，但我需要显示所有列：

select ls.subscriberid as id, l.name as list_name, 
  ifnull(cfn.first_name, '') as first_name, 
  ifnull(cln.last_name, '') as last_name, 
  ifnull(ce.email_address, '') as email_address, 
  ifnull(cm.mobile_phone, '') as mobile_phone
from (
    select ls.subscriberid, ifnull(s.data, '') as first_name
    from subscribers_data s
      right outer join list_subscribers ls on ls.subscriberid = s.subscriberid
    where s.fieldid = 2 /* First Name */
) cfn
right outer join (
    select ls.subscriberid, ifnull(s.data, '') as last_name
    from subscribers_data s
      right outer join list_subscribers ls on ls.subscriberid = s.subscriberid
    where s.fieldid = 3 /* Last Name */
) cln on cfn.subscriberid = cln.subscriberid
right outer join (
    select ls.subscriberid, ls.emailaddress as email_address
    from list_subscribers ls
) ce on ce.subscriberid = cfn.subscriberid
right outer join (
    select ls.subscriberid, ifnull(s.data, '') as mobile_phone
    from subscribers_data s
      right outer join list_subscribers ls on ls.subscriberid = s.subscriberid
    where s.fieldid = 81 /* Mobile Phone */
) cm on cm.subscriberid = cfn.subscriberid
right outer join list_subscribers ls on ls.subscriberid = cfn.subscriberid
inner join lists l on ls.listid = l.listid

【问题讨论】：

标签： mysql views subquery

【解决方案1】：

试试这个：

SELECT ls.subscriberid as id, l.name as list_name, 
       ifnull(group_concat(CASE WHEN s.fieldId = 2 
                                THEN s.data 
                                ELSE NULL 
                           END), '') as first_name, 
       ifnull(group_concat(CASE WHEN s.fieldId = 3
                                THEN s.data 
                                ELSE NULL 
                           END), '') as last_name, 
       ifnull(ls.email_address, '') as email_address, 
       ifnull(group_concat(CASE WHEN s.fieldId = 81
                                THEN s.data 
                                ELSE NULL 
                           END), '') as mobile_phone
  FROM list_subscribers ls
INNER JOIN lists l on ls.listid = l.listid
 LEFT JOIN subscribers_data s on ls.subscriberid = s.subscriberid
  GROUP BY ls.subscriberid, l.name, ls.email_address

【讨论】：