Question

将两个查询合并为一个是否有效？有什么优点或缺点？有人可以帮我把这两个问题结合起来：

SELECT quiz_id from questions WHERE question = 10

SELECT quiz_number FROM quizzes WHERE quiz_id = 5

quiz_id与问题有1对多的关系。因此，对于一个特定问题，将只有一个quiz_id，但一个quiz_id可能最多有20个问题。

Answer 1

不确定 combine 的含义，或许你的意思是subselect / subquery？在这种情况下，尝试：

---    IN syntax
SELECT quiz_number FROM quizzes WHERE quiz_id IN
       (SELECT quiz_id FROM questions WHERE question = 10);

---    = syntax. This will work only if the subquery returns one value 
SELECT quiz_number FROM quizzes WHERE quiz_id = 
       (SELECT quiz_id FROM questions WHERE question = 10);

Answer 2

假设您发布的2个查询的关系，以及第二个查询中的值5是第一个查询的结果：

SELECT quiz_number FROM quizzes qz
INNER JOIN questions qu on qu.quiz_id = qz.quiz_id
WHERE question = 10

Answer 3

你可以使用别名

SELECT question.quiz_id, quiz.quiz_number from questions question,quizzes quiz WHERE question.question = 10 and quiz.quiz_id =5

有没有办法结合这些查询

3 个答案: