MySQL - 我的视图很慢

Question

我有 4 张桌子：

• 学生 with over 7000 records
• 教师 with over 600 records
• 大学 with over 30 records
• Lessons_Meta with over 10000 records

表学生列：

id | student_number | name

表 Teachers 列：

id | teacher_number | name

表大学列：

id | name

表 Lessons_Meta 列：

id | lesson_code | lesson_name | student_id | teacher_id | university_id

我的看法是：

CREATE VIEW `view_lessons` AS
SELECT
        *,
        (SELECT `name` FROM `students` WHERE `students`.`id` = `lessons_meta`.`student_id` LIMIT 1) AS "student_name",
        (SELECT `name` FROM `teachers` WHERE `teachers`.`id` = `lessons_meta`.`teacher_id` LIMIT 1) AS "teacher_name",
        (SELECT `name` FROM `universities` WHERE `universities`.`id` = `lessons_meta`.`university_id` LIMIT 1) AS "university_name"
FROM `lessons_meta`

我的查询是：

SELECT * FROM `view_lessons` LIMIT 20

20 秒后，显示此查询已完成！我怎样才能减少这个时间负载？

Answer 1

您可能只需要索引。从以下索引开始：

CREATE INDEX idx_students_id_name ON students(id, name);
CREATE INDEX idx_teachers_id_name ON teachers(id, name);
CREATE INDEX idx_universities_id_name ON universities(id, name);

Answer 2

将您的视图更改为此

CREATE VIEW `view_lessons` AS
SELECT L.*,  S.`name` AS student_name, T.`name` AS teacher_name, U.`name` AS university_name
FROM `lessons_meta` L
INNER JOIN `students` S ON S.`id` = L.`student_id`
INNER JOIN `teachers` T ON T.`id` = L.`teacher_id` 
INNER JOIN `universities` U ON U.`id` = L.`university_id`

• 在lessons_meta 表中，在student_id、teacher_id、university_id 上添加索引
• 在所有表上，确保 id 列被正确索引，通常它们应该是唯一的/PK