我有五张桌子，这是一个很大的混乱，我试图加入。
Tbl - USERS
id - name
---------
1
2
3
4
5
Tbl - SESSION1
id | user_id | date
--------------------
1 1 1/1/11
2 2 1/2/11
3 3 1/2/11
4 5 1/3/11
Tbl - SESSION2
id | user_id | date
--------------------
1 1 1/1/12
2 2 1/1/12
3 4 1/2/12
5 5 1/2/12
Table - QA
id | user_id | session_id | question | answer
--------------------------------------------------------------------
1 1 1 Did you go on vacation? Y
2 1 1 Did you like it there? N
3 1 2 Did you have travel insurance? N
4 3 1 Did you go on vacation? Y
5 3 1 Did you like it there? N
6 3 1 Did you have travel insurance? N
Table - QA2
id | user_id | session_id | question | answer
--------------------------------------------------------
1 1 1 Country Visited Cuba
2 1 2 Country Visited Mexico
我想运行一个查询，以便在连接中获得以下数据，这是最有效的。我需要检查用户是否回答了问题，“你去过度假吗。”
user_id | session 1 | session 2 | question | answer | country
---------------------------------------------------------------------------
1 1/1/11 null been on vacation yes cuba
1 1/1/11 null had travel insurance no cuba
1 null 1/1/12 been on vacation yes mexico
1 null 1/1/12 had travel insurance no mexico
更新/免责声明：我没有设计此架构，我无法进行更改。