使用join從2個以上的mysql表中獲取數據。

Question

這是我的表格結構。

Table1  // it has 4 colums,that saves all the question posted by user

id|question|answer|postby|

Table2  //it has 2 colums, that saves all the signed up users

id|username|email|

Table3 //it saves that which question is read by which user.

id|reader_id|question_id| 

注意：reader_id是表2的ID。

問題：我們需要找出特定用戶沒有閱讀的那些問題。

Answer 1

select * from table1 where id not in (
    select question_id from table3 where reader_id = [particular user id]
)

Answer 2

從表1中選擇ID不輸入的問題（在表1中選擇問題ID的讀者（在用戶名='XXXX'的情況下從表2選擇的ID））

Answer 3

嘗試這個：

SELECT t1.*
FROM table1 t1
LEFT JOIN
  (SELECT t3.* 
   FROM 
   table2 t2
   JOIN table3 t3 ON t3.reader_id=t2.id
   WHERE t3.reader_id=SOME USER)t ON t.question_id=t1.id
WHERE t3.id IS NULL;