根据主键表的主键获取外键表行的行数

Question

与PK和Fk关系一样。

我有两个表，一个是让我们说items_info，第二个是poll_report

items_info 结构如下

 _id       Autogenerated integer based PK

Question   varchar(255) 

poll_report

_id       Autogenerated integer based PK

questionId FK to prev table's _id

answerId  integer

deviceId  UNIQUE

我想使用单个查询获取以下类型的数据。

items_info._id   |  items_info.Question  |  count(poll_report.answerId) where poll_report.answerId  == 1 |  count(poll_report.answerId) where poll_report.answerId == 2

你能帮帮我吗？

Answer 1

你可能想要这样的东西：

select items_info._id , items_info.Question , sum(poll_report.answerId =1) , sum(poll_report.answerId =2) from items_info,poll_report where items_info._id=poll_report.questionId group by items_info._id;

无论如何，关键是你可以这样做：

sum(poll_report.answerId = 1)