使用不同的 where 子句加入 2 个表

Question

我的数据库中有 2 个表

1.admin_store_exam 列是 exam_name、A_QNum、math_ques、math_a、math_b、math_c、math_d、A_Ans

2.student_ans_history 列是 考试名称、S_ID、S_QNum、S_Ans、S_Noans

现在我想用不同的 WHERE 子句在 exam_name 列上加入这两个表。

这里有两个不同的带有 WHERE 子句的查询。

$sql="SELECT * FROM admin_store_exam WHERE exam_name='$en'";

$sql="SELECT * FROM student_ans_history WHERE exam_name='$en' AND S_ID='$session_contact'";

加入这两个表后，我得到了这些。

$sql="
SELECT admin_store_exam.A_QNum
     , admin_store_exam.math_ques
     , admin_store_exam.math_a
     , admin_store_exam.math_b
     , admin_store_exam.math_c
     , admin_store_exam.math_d
     , admin_store_exam.A_Ans
     , student_ans_history.S_Ans
     , student_ans_history.S_Noans 
  FROM admin_store_exam 
 WHERE admin_store_exam.exam_name = '$en' 
  JOIN student_ans_history 
 WHERE student_ans_history.exam_name = '$en' 
   AND S_ID = '$session_contact' 
    ON admin_store_exam.exam_name = student_ans_history.exam_name
 ";

但不幸的是，我不会得到任何结果。 我对sql不是很熟悉，所以不明白我在哪里做错了。谁能帮我解决这个问题。谢谢..

Answer 1

你可以像这样加入它：

$sql="SELECT admin_store_exam.A_QNum
 , admin_store_exam.math_ques
 , admin_store_exam.math_a
 , admin_store_exam.math_b
 , admin_store_exam.math_c
 , admin_store_exam.math_d
 , admin_store_exam.A_Ans
 , CONCAT(S_Ans,S_Noans) AS S_Ans
  FROM admin_store_exam 
 INNER 
  JOIN student_ans_history 
    ON admin_store_exam.exam_name = student_ans_history.exam_name 
        AND admin_store_exam.A_QNum = student_ans_history.S_QNum
 WHERE admin_store_exam.exam_name = '$en' 
   AND student_ans_history.S_ID = '$session_contact'
    GROUP BY admin_store_exam.exam_name, admin_store_exam.A_QNum";

希望这行得通！！！

Answer 2

您可以使用子查询。考虑以下示例：

SELECT A.* FROM
(SELECT * FROM admin_store_exam WHERE exam_name='AB') AS A
INNER JOIN
(SELECT * FROM student_ans_history WHERE exam_name='AB' AND S_ID='23344') AS B
ON A.exam_name = B.exam_name