相关疑难解决方法(0)

只是好奇SQL语法.所以,如果我有

SELECT 
 itemName as ItemName,
 substring(itemName, 1,1) as FirstLetter,
 Count(itemName)
FROM table1
GROUP BY itemName, FirstLetter

这是不正确的,因为

GROUP BY itemName, FirstLetter 

真的应该

GROUP BY itemName, substring(itemName, 1,1)

但为什么我们不能简单地使用前者来方便呢？

我想做这样的事情:

SELECT round(100*(col_a - col_b)/col_a, 1) as Foo, Foo - col_c as Bar
FROM my_table
WHERE...;

但是,我得到一个错误说Foo不明.由于Foo是从一堆其他列的某些计算得出的,所以我不想再重复该公式Bar.任何解决方法？

select SUM (Bill) from ProductSaleReport group by PCI 
having MONTH(Date) between 1 and 3

任何人都可以帮我找到问题.

我收到错误:

消息8121,级别16,状态1,行1
列'ProductSaleReport.Date'在HAVING子句中无效,因为它不包含在聚合函数或GROUP BY子句中.
消息8121,级别16,状态1,行1
列'ProductSaleReport.Date'在HAVING子句中无效,因为它不包含在聚合函数或GROUP BY子句中.

在 Oracle 中，首先评估哪些子句类型？如果我有以下内容（假装 .... 代表有效的表达式和关系名称），评估的顺序是什么？

SELECT   ...
FROM     .....
WHERE    ........
GROUP BY ...........
HAVING   .............
ORDER BY ................

我的印象是 SELECT 子句是最后评估的，但除此之外我一无所知。

SELECT *,DAYNAME(created_on) AS created_day FROM users_feedback WHERE created_day = 'wednesday'

当我执行上面的查询时,它会生成如下错误

Error Code : 1054
Unknown column 'created_day' in 'where clause'

Execution Time : 00:00:00:000
Transfer Time  : 00:00:00:000
Total Time     : 00:00:00:000

为什么两个查询的结果相同？(我正在使用northwind数据库.)

SELECT      ContactTitle
        ,   COUNT(CustomerID) AS NumberOfCustomer
FROM        dbo.Customers
WHERE       ContactTitle LIKE '%sales%'
GROUP BY    ContactTitle
HAVING      COUNT(*) >= 5
ORDER BY    NumberOfCustomer desc

和

SELECT 
DISTINCT    ContactTitle
        ,   COUNT(CustomerID) AS NumberOfCustomer
FROM        dbo.Customers
WHERE       ContactTitle LIKE '%sales%'
GROUP BY    ContactTitle
HAVING      COUNT(*) >= 5
ORDER BY    NumberOfCustomer desc

结果是:

ContactTitle           NumberOfCustomer
---------------------  ----------------
Sales Representative         17
Sales Manager                11
Sales Associate               7
Sales Agent                   5

根据我自己的理解,第二个查询得到不同的标题并计算其记录,所以我期望结果将是无,因为每个标题只有记录计数1.我是对的吗？

我正在编写一个mysql查询并收到错误.

"'字段列表'中的未知列'dat'"

由于在mysql的IF条件中使用别名而发生此错误.

这是mysql查询:

SELECT 
    nCustomerID,
    dDateRegistered,
    (select count(nPlayerID) from credit_logs 
        where nPlayerID=nCustomerID) as total_clog,
    (select count(nPlayerID) FROM bl_transaction_history
        where nPlayerID=nCustomerID) as total_tran,
    (select count(nCustomerID) from customer_freeplays
        where nCustomerID=nCustomerID) as total_free,
    (select dDateAdded from bl_transaction_history
        where nPlayerID=nCustomerID) as dat,
    (select DATEDIFF(now(),dat)/30 ) as date_differece1,
    (select DATEDIFF(now(),dDateRegistered)/30 ) as date_difference2,
    IF (dat IS NOT NULL,(select DATEDIFF(now(),dat)/30 ),
        (select DATEDIFF(now(),dDateRegistered)/30 )) as date_difference
FROM bl_customers
WHERE nAccountStatus=1 
  and bDeleted=0 
having total_clog>0 
    or total_tran>0 
    or total_free>0

任何帮助都会被appriciated .. :)

提前致谢.

之后到底有什么关系？我的意思是如果我这样做

SELECT * FROM  table GROUP BY x ORDER BY y

首先将结果分组然后排序？

我有一个表(很大的一个)有很多列,其中两个是"post"和"user".对于给定的"帖子",我想知道哪个"用户"发布最多.

我首先考虑获取所有条目WHERE(post ='wanted_post'),然后抛出一个PHP hack来查找我得到的最大"用户"值,但考虑到我的表的大小,以及我对MySQL的了解不足微妙的调用,我正在寻找一种纯MySQL的方式来获得这个值(基本上在给定的"帖子"上发布最多的"用户"id).

可能吗 ？或者我应该依靠混合SQL-PHP解决方案？

谢谢,Cystack