Mysql 使用联接优化查询
如何使用联接完成查询。我是数据库新手。这个查询运行良好。。 但我想让它更鲁布斯特Mysql 使用联接优化查询,mysql,sql,join,refactoring,Mysql,Sql,Join,Refactoring,如何使用联接完成查询。我是数据库新手。这个查询运行良好。。 但我想让它更鲁布斯特 $query = "SELECT student_id FROM students WHERE student_id IN ( SELECT student_id FROM class_students WHERE class_id IN ( SELECT class_id FROM class_course
$query = "SELECT student_id
FROM students
WHERE student_id
IN (
SELECT student_id
FROM class_students
WHERE class_id
IN (
SELECT class_id
FROM class_course
WHERE teacher_id =". $_SESSION['teacher_id']."))";
是否有其他方法可以将使用中的转换为正确的联接:
$query = "select students.student_id
from class_course left outer join class_students on
class_course.class_id = class_students.class_id
left outer join students on
class_students.student_id = students.student_id
where class_course.teacher_id = ". $_SESSION['teacher_id']
SELECT s.student_id
FROM students s
JOIN class_students cs ON cs.student_id = s.student_id
JOIN class_course c ON c.class_id = cs.class_id
WHERE teacher_id = ?
请注意,我已经删除了(不相关的)应用程序语言规范(perl?),只留下回答问题的SQL。Yes。参见连接。这就是他们的目的。这里有一个关于和
$query = "SELECT s.student_id
FROM students s
INNER JOIN class_students cs
ON s.student_id = cs.student_id
INNER JOIN class_course cc
ON cs.class_id = cc.class_id
AND cc.teacher_id =". $_SESSION['teacher_id']."))