Question

我正在制作一个事件应用程序，该程序可让人们一起创建具有名称，数量和价格的事件和票证类型，当用户购买票证时，所购买的交易会插入到不同的表格中，购买交易中包含{ {1}}，event ID和其他字段。此时，我想使用ticket type ID，ticket type name，quantity和price来获取我的所有票证类型。

这是我的桌子的图形外观

available tickets

我想要的输出是

TicketTypeTable
---------------------------------
|id |eventfk | name | qty | price|
|--------------------------------|


TicketSalesTable
----------------------------------------------
|id |userfk |eventfk | ticketype | qty | price|
|---------------------------------------------|`

我可以使用-------------------------------------------- |id |eventfk | name | qty |available | price| |-------------------------------------------|这样的

inner select

但是这对于大型数据库是不利的……无论情况如何，这都是有害的。

有人知道更好的出路吗？

我也尝试过使用JOIN但被卡住了

select id , eventfk , name , qty (select count(*) from ticketsalestable) available , price from tickettypetable

Answer 1

我认为您希望加入票务合计的集合，例如

SELECT t.id, t.eventfk, t.name, t.quantity, t.price, (t.qty - s.sold) as available FROM tickettypetable t LEFT JOIN 
    ( select eventfk, tickettype, sum(qty) as sold from ticketsalestable group by eventfk, tickettype) s
    ON s.eventfk = t.eventfk and t.id = s.tickettype
 WHERE t.eventfk = 10

取决于优化程序，将where条件也添加到聚合中可能更快

SELECT t.id, t.eventfk, t.name, t.quantity, t.price, (t.qty - s.sold) as available FROM tickettypetable t LEFT JOIN 
    ( select eventfk, tickettype, sum(qty) as sold from ticketsalestable group by eventfk, tickettype where eventfk = 10) s
    ON s.eventfk = t.eventfk and t.id = s.tickettype
 WHERE t.eventfk = 10

编辑票证也是加入条件

Answer 2

基于Turo's的答案，我对其进行了修改，并提出了这个建议

SELECT t.id, t.name, t.quantity, IF(t.price = 0,'FREE',t.price), (t.quantity - IFNULL(s.sold, 0)) as available FROM tickettypetb t LEFT JOIN (select sl.eventfk, sl.tickettypefk, COUNT(sl.eventfk) as sold from salestb sl GROUP BY sl.tickettypefk ORDER BY sl.tickettypefk DESC) s ON s.tickettypefk = t.id AND s.eventfk = t.eventfk WHERE t.eventfk = 22 GROUP BY t.id ORDER BY t.id DESC

SQL，避免使用内部选择

2 个答案: