Question

我有一个带有时间戳字段'bar'的表'foo'。如何获取查询的最旧时间戳，例如：来自foo的SELECT foo.bar？我试过做类似的事情：来自foo的SELECT MIN（foo.bar），但它失败并出现此错误

第1行的错误1140（42000）：如果没有GROUP BY子句，则GROUP GROUP列（MIN（），MAX（），COUNT（），...）的混合没有GROUP列是非法的

好的，所以我的查询比这复杂得多，这就是为什么我很难用它。这是使用MIN（a.timestamp）：

的查询

select distinct a.user_id as 'User ID',
       a.project_id as 'Remix Project Id',
       prjs.based_on_pid as 'Original Project ID',
       (case when f.reasons is NULL then 'N' else 'Y' end)
         as 'Flagged Y or N',
       f.reasons, f.timestamp, MIN(a.timestamp) 
from view_stats a
     join (select id, based_on_pid, user_id
                    from projects p) prjs on
     (a.project_id = prjs.id)
     left outer join flaggers f on
     (    f.project_id = a.project_id
      and f.user_id = a.user_id)
where a.project_id in
(select distinct b.id
   from projects b
  where b.based_on_pid in
                ( select distinct c.id
                    from projects c
                   where c.user_id = a.user_id
                )
)
order by f.reasons desc, a.user_id, a.project_id;

非常感谢任何帮助。

view_stats表：

+------------+------------------+------+-----+-------------------+----------------+
| Field      | Type             | Null | Key | Default           | Extra          |
+------------+------------------+------+-----+-------------------+----------------+
| id         | int(10) unsigned | NO   | PRI | NULL              | auto_increment | 
| user_id    | int(10) unsigned | NO   | MUL | 0                 |                | 
| project_id | int(10) unsigned | NO   | MUL | 0                 |                | 
| ipaddress  | bigint(20)       | YES  | MUL | NULL              |                | 
| timestamp  | timestamp        | NO   |     | CURRENT_TIMESTAMP |                | 
+------------+------------------+------+-----+-------------------+----------------+

更新

Based on thomas' suggestion I converted my query to:
select distinct a.user_id as 'User ID',
       a.project_id as 'Remix Project Id',
       prjs.based_on_pid as 'Original Project ID',
       (case when f.reasons is NULL then 'N' else 'Y' end)
         as 'Flagged Y or N',
       f.reasons, f.timestamp, min(a.timestamp)
from view_stats a
     join (select id, based_on_pid, user_id
                    from projects p) prjs on
     (a.project_id = prjs.id)
     left outer join flaggers f on
     (    f.project_id = a.project_id
      and f.user_id = a.user_id)
where a.project_id in
(select distinct b.id
   from projects b
  where b.based_on_pid in
                ( select distinct c.id
                    from projects c
                   where c.user_id = a.user_id
                )
)
group by a.project_id, a.user_id
order by a.timestamp
;

现在正在运行。

Answer 1

如果你要使用聚合函数（如min（），max（），avg（）等），你需要告诉数据库它需要采用min（）的确切内容。

transaction    date
one            8/4/09
one            8/5/09
one            8/6/09
two            8/1/09
two            8/3/09
three          8/4/09

我假设你想要以下内容。

transaction    date
one            8/4/09
two            8/1/09
three          8/4/09

然后为了得到它你可以使用以下查询...注意group by子句告诉数据库如何对数据进行分组并得到某些东西的min（）。

select
    transaction,
    min(date)
from
    table
group by
    transaction

帮助特定的MySQL查询：如何从一组多个值中获取最小值

1 个答案: