[英]MySQL - Inner join with WHERE clause
我在查找有條件的記錄時遇到了問題。 我想找到所有帶有標志的課程。
課程表記錄:
+----+------+-----------------+
| id | code | name |
+----+------+-----------------+
| 1 | JPA | JPA Lorem ipsum |
| 2 | JSF | Jsf lorem ipsum |
+----+------+-----------------+
course_flags表的記錄:
+----+-----------+---------+
| id | course_id | flag_id |
+----+-----------+---------+
| 1 | 1 | 1 |
| 2 | 1 | 2 |
+----+-----------+---------+
SELECT `course`.`id`, `course`.`name` FROM `course`
INNER JOIN `course_flags`
ON `course` .`id` = `course_flags`.`course_id`
WHERE (`course_flags`.`flags_id` = 1)
數據庫返回:
+----+-----------------+
| id | name |
+----+-----------------+
| 1 | JPA Lorem ipsum |
+----+-----------------+
SELECT `course`.`id`, `course`.`name` FROM `course`
INNER JOIN `course_flags`
ON `course` .`id` = `course_flags`.`course_id`
WHERE (`course_flags`.`flags_id` = 1 and `course_flags`.`flags_id` = 2)
數據庫返回:
null
我想收到:
+----+-----------------+
| id | name |
+----+-----------------+
| 1 | JPA Lorem ipsum |
+----+-----------------+
問題我如何得到?
提前致謝!
SELECT c.id, c.name
FROM course AS c
INNER JOIN course_flags AS cf
ON c.id = cf.course_id
WHERE cf.flags_id = 1
OR cf.flags_id = 2
我懷疑您希望所有提供所有標志的課程。
您可以通過在聯接中添加一個或條件,然后檢查標志的數量是否符合您的期望來做到這一點:
SELECT `course`.`id`, `course`.`name` FROM `course`
INNER JOIN `course_flags`
ON `course` .`id` = `course_flags`.`course_id`
AND (`course_flags`.`flags_id` = 1 OR `course_flags`.`flags_id` = 2)
WHERE
GROUP BY (course.id)
HAVING COUNT(DISTINCT course_flags.id) = 2;
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