根據主鍵表的主鍵獲取外鍵表的行數

Question

照常在PK和Fk關系中。

我有兩個表，一個是說items_info ，第二個是poll_report

items_info結構如下

 _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

我想使用單個查詢獲取以下類型的數據。

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

你能幫我么 ？

Answer 1

您可能想要這樣的東西：

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;

無論如何，關鍵的是您可以執行以下操作：

sum(poll_report.answerId = 1)