Question

我的问题是我想要算上 n 部门下的所有学生。
注意：学生有一门课程，课程有自己的部门（一个部门有很多课程）。 样品输出：

+---------+-------------------------------+ | student | department | +---------+-------------------------------+ | 23| Computer Education Department | | 67| Basic Education Department | | 39| Mathematics Department | | 40| Humanities Department | | 61| Engineering Department | | 79| Management Department | +---------+-------------------------------+

tbl_students

+---------+---------------+--------+ | stud_id | name | course | +---------+---------------+--------+ | 1 | Jack Owen | 1 | | 2 | Kirby Lopez | 2 | | 3 | Justin Minus | 1 | | 4 | Jerome Noveda | 1 | +---------+---------------+--------+

2。 tbl_courses

+-----------+------------+---------+ | course_id | short_name | dept_id | +-----------+------------+---------+ | 1 | BSIT | 1 | | 2 | BSCS | 1 | | 3 | BEED | 2 | | 4 | BSED | 2 | | 6 | BSTHRM | 7 | | 7 | BLIS | 4 | | 8 | BSCE | 6 | +-----------+------------+---------+

3。 tbl_department

+---------+-------------------------------+ | dept_id | full_name | +---------+-------------------------------+ | 1 | Computer Education Department | | 2 | Basic Education Department | | 3 | Mathematics Department | | 4 | Humanities Department | | 6 | Engineering Department | | 7 | Management Department | +---------+-------------------------------+

Answer 1

我认为你可以这样做：

SELECT
    tbl_department.full_name as department,
    COUNT(DISTINCT tbl_students.stud_id) AS student
FROM
    tbl_department
    JOIN tbl_courses
        ON tbl_department.dept_id = tbl_courses.dept_id
    JOIN tbl_students
        ON tbl_courses.course_id = tbl_students.course
GROUP BY
    tbl_department.full_name

Answer 2

SELECT 
ISNULL(( SELECT COUNT(*) FROM tbl_courses C
  INNER JOIN tbl_students S ON C.course_id = S.course
  WHERE C.dept_id = D.dept_id
),0) AS student
,D.full_name AS department
FROM
tbl_department D

我希望它对你有用。

SQL表 - 根据其他2个表的条件计算table1的行

2 个答案: