为什么你需要把你自己创建的(例如列select 1 as "number"后)HAVING,而不是WHERE在MySQL？

是否有任何缺点而不是做WHERE 1(编写整个定义而不是列名)？

这两个查询有什么区别？

SELECT f.name, 
       u.name, 
       u.id 
FROM   families f 
       JOIN units u 
         ON f.unit_id = u.id 
HAVING u.id IN( 43, 413, 22 )

和:

SELECT f.name, 
       u.name, 
       u.id 
FROM   families f 
       JOIN units u 
         ON f.unit_id = u.id 
WHERE  u.id IN( 43, 413, 22 )

这两个查询的结果完全相同.那么区别在哪里？

有没有可能做这样的事情？

SELECT 
    @z:=SUM(item),
    2*@z
FROM
    TableA;

对于第二列,我总是得到NULL.奇怪的是,在做某事的同时

SELECT 
    @z:=someProcedure(item),
    2*@z
FROM
    TableA;

一切都按预期工作.为什么？

我试图在Arel和/或Rails 3中的Active Record中嵌套SELECT查询以生成以下SQL语句.

SELECT sorted.* FROM (SELECT * FROM points ORDER BY points.timestamp DESC) AS sorted GROUP BY sorted.client_id

可以通过执行创建子查询的别名

points = Table(:points)
sorted = points.order('timestamp DESC').alias

但后来我被困在如何将它传递给父查询(缺少调用#to_sql,这听起来很难看).

如何使用SELECT语句作为Arel(或Active Record)中的子查询来完成上述操作？也许有一种完全不同的方式来完成这个不使用嵌套查询的查询？

我试图在两个表中为一些完整性编写一些查询.查询是这样的

SELECT if( o.is_discounted !=1, o.item_cost, o.discounted_item_cost ) AS order_item_total,
SUM( oi.quantity * oi.price ) AS item_total
FROM orders o
INNER JOIN order_items oi ON oi.order_id = o.id
WHERE order_item_total != item_total
GROUP BY o.id

我过去肯定会在这些列中使用别名,所以我不确定为什么在这种情况下它告诉我order_item_total不是列.

我有这样的查询:

SELECT User.id, 10*10 as distance
FROM USERS
INNER JOIN
(
    SELECT Location.user_id,
    min(10 * 10) as mindistance
    FROM Location
    GROUP BY Location.user_id
 ) L ON Users.id = Location.user_id AND distance = L.mindistance

如果我保持原样,我会继续:

Unknown column 'distance' in 'on clause'

但如果我把User.distance而不仅仅是距离,我得到:

MySQL syntax error near....

我不能在计算字段上以这种方式使用别名吗？10*10只是一个简单的占位符,因为计算要复杂得多.

我有一个像这样的结果集:

ID | name  | myvalue
 1 | A1    | 22
 2 | A2    | 22
 3 | A3    | 21
 4 | A4    | 33
 5 | A5    | 33
 6 | A6    | 10
 7 | A7    | 10
 8 | A8    | 10
 9 | A9    | 5

我想要的是,只包括包含最高"myvalue"的行(在前面的例子中是33),然后:

ID | name  | myvalue
 4 | A4    | 33
 5 | A5    | 33

IE查询应该选择最高的"myvalue"(IE 33),它应该删除myvalue <33的行

SELECT ..... WHERE myvalue = THE_HIGHEST_OF(myvalue)

希望能够清楚......

先感谢您

编辑:

我目前的查询是 …

我试图减去2个别名,以便创建另一个别名,但我得到一个"未知列"错误.

这是我的SQL:

select o.id, o.name,
     (select sum(l.source_expense)
        from `assignments` as a
        left join `leads` as l on (l.id = a.lead_id)
        where a.{$this->sql_column}=o.id
        and l.date_created between {$this->date_from} and {$this->date_to}
        and find_in_set(l.vertical_id, '".implode(',', $this->app_user->verticals)."')
     ) as `expense`,
     (select sum(a.buyer_revenue)
        from `assignments` as a
        left join `leads` as l on (l.id = a.lead_id)
        where a.refunded=0
        and a.{$this->sql_column}=o.id
        and l.date_created between {$this->date_from} and {$this->date_to}
        and find_in_set(l.vertical_id, '".implode(',', $this->app_user->verticals)."')
     ) as `revenue`,
     `revenue` - `expense` as `profit`
     from {$this->sql_table} as o

基本上,我想profit通过减去revenue …

我的查询有问题,

SELECT id, pseudo, nom, prenom, sexe, ville, 
       FLOOR(DATEDIFF (NOW(), date_naissance)/365) AS mAge 
FROM user 
WHERE sexe = 'Homme' AND mAge BETWEEN 18 AND 25 OR ville = 'Bordeaux'

它应该返回匹配用户的where条件.问题是如下,mAge不存在我得到以下错误:

1054 - 'where子句'中的未知列'mAge'

看起来我的别名在where条件下无法正常工作.

如果我删除了mAge WHERE CLAUSE,我成功获得了mAge别名.

我需要你们

提前致谢 !