Question

在我的查询中，我列出了不同客户的所有剧院门票销售和电影票销售。我遇到的问题是所有的＆＃39; 0＆＃39;门票销售，所以没有出现剧院门票或电影票的用户没有出现。

这是一张视觉方面的图片：table

我相信我需要做一个工会才能让那些没有购买任何门票的用户返回。我似乎无法解决这个问题。

提前致谢。

到目前为止，这是我的代码：

select customer.hippcode, customer.LastName, customer.Firstname, customer.Email,
count(ticketdetails.eventtype) as 'Theater Tickets',
0 as 'Movie Tickets'
from customer
inner join ticketdetails on ticketdetails.hippcode = customer.hippcode
where ticketdetails.hippcode is not null
and ticketdetails.eventType ='T'
Group by Customer.hippcode
union 
select customer.hippcode, customer.LastName, customer.Firstname, customer.Email,
0 as 'Theater Tickets', count(ticketdetails.eventtype) as 'Movie Tickets'
from customer
inner join ticketdetails on ticketdetails.hippcode = customer.hippcode
where ticketdetails.hippcode is not null
and ticketdetails.eventType ='M'
Group by Customer.hippcode
order by `theater tickets` + `movie tickets` desc;
select 
    customer.hippcode, customer.LastName, customer.Firstname, customer.Email,
    sum(case when ticketdetails.eventtype = 'T' then 1 else 0 end) as TheaterTickets,
    sum(case when ticketdetails.eventtype = 'M' then 1 else 0 end) as MovieTickets
from customer
inner join ticketdetails on ticketdetails.hippcode = customer.hippcode
where ticketdetails.hippcode is not null
and ticketdetails.eventType in ('T', 'M')
Group by customer.hippcode, customer.LastName, customer.Firstname, customer.Email
Order by 'TheaterTickets' + 'MovieTickets' desc

Answer 1

inner join =＆gt;只有当你在两张桌子上都有记录时才能上线。

我认为您应该使用LEFT JOIN某处选择主表

http://dev.mysql.com/doc/refman/5.7/en/join.html和 http://dev.mysql.com/doc/refman/5.7/en/left-join-optimization.html

Answer 2

我认为最后一个查询是您唯一想要的查询。 where是合适的，但您需要注意select c.hippcode, c.LastName, c.Firstname, c.Email, sum(td.eventtype) as TheaterTickets, sum(td.eventtype) as MovieTickets from customer c left join ticketdetails td on td.hippcode = c.hippcode and td.eventType in ('T', 'M') Group by c.hippcode, c.LastName, c.Firstname, c.Email Order by count(t.hippcode) desc;子句：

ticketdetails

注意：

表别名使查询更易于阅读和写入。
on上的条件包含where子句，而不是td.hippcode is not null子句。
NULL上的条件是不必要的，因为join中case不匹配（注意：您可能需要检查客户列）。
order by 0是进行条件求和的标准方法（因此也是正确的）。但是，MySQL提供了一种更简单直观的语法。
你的订单没有做任何事，因为它添加了两个字符串（因此相当于url。不要使用单引号永远作为列名，你不会有像这样的问题。

查询没有显示0值mysql

2 个答案: