refactor: 更改子查询为join

src/main/resources/mapper/course/CourseDao.xml

@@ -47,8 +47,16 @@
         FROM
         course AS c
         LEFT JOIN course_classification AS cc ON c.classify_id = cc.classification_id
-        left join banner as b on b.id=c.banner_id
-        left join (select course_id,count(*) as courseDetailsCount from course_details group by course_id) d.course_id = c.course_id
+        LEFT JOIN banner AS b ON b.id = c.banner_id
+        LEFT JOIN (
+        SELECT
+        course_id,
+        COUNT(*) AS courseDetailsCount
+        FROM
+        course_details
+        GROUP BY
+        course_id
+        ) AS d ON d.course_id = c.course_id
         WHERE
         1 = 1
         AND c.is_delete = 0