[英]Getting the most recent row and linking it with another table?
我正在尝试获取表的最新行
user_quiz:
+--------+-----------+-------------+-------------------+------------+
|quiz_id |userid | module_id |number_of_questions| user_score |
+--------+-----------+-------------+-------------------+-------- ---+
| 1 | 1 | 1 | 5 | 5 |
| 2 | 2 | 2 | 10 | 9 |
| 3 | 1 | 1 | 10 | 9 |
+--------+-----------+-------------+-------------------+------------+
我用过查询:
SELECT * FROM user_quiz WHERE userid = 1 ORDER BY quiz_id DESC LIMIT 1
正确检索最后一行。 但是我想将module_id与另一个表链接:
module:
+---------+------------+
|module_id|module_name |
+---------+------------+
| 1 | Forces |
| 2 | Electricity|
+---------+------------+
并获取模块名称。
查询结果将用于打印用户最近的测验:
Most recent quiz: Forces - Number of questions: 10 - User Score: 9
仅使用一个查询就能做到吗?
您只需要一个JOIN
:
SELECT uq.*, m.module_name
FROM user_quiz uq JOIN
modules m
ON uq.module_id = m.module_id
WHERE uq.userid = 1
ORDER BY uq.quiz_id DESC
LIMIT 1;
一个更简单的查询来达到相同的效果是
SELECT
user_quiz.quiz_id,
user_quiz.number_of_questions,
user_quiz.user_score,
modules .module_name
FROM user_quiz JOIN modules
ON user_quiz.module_id = modules.module_id
WHERE user_quiz.userid = 1
ORDER BY user_quiz.quiz_id DESC
LIMIT 1
如果要为所有用户获得相同的结果,则可以使用更复杂的查询
SELECT
user_quiz_virtual_table.userid,
user_quiz_virtual_table.quiz_id,
user_quiz_virtual_table.number_of_questions,
user_quiz_virtual_table.user_score,
modules.module_name
FROM (
SELECT
user_quiz.userid
user_quiz.quiz_id,
user_quiz.module_id
user_quiz.number_of_questions,
user_quiz.user_score
FROM user_quiz
ORDER BY user_quiz.quiz_id DESC
GROUP BY userid
) AS user_quiz_virtual_table
JOIN modules ON user_quiz_virtual_table.module_id = modules.module_id
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