如何合并两个表中的两个选择？

Question

This is my DB schema:

CREATE TABLE `members` (
  `m_id` int NOT NULL AUTO_INCREMENT,
  `m_name` varchar(355),
  `m_email` varchar(20) UNIQUE,
  PRIMARY KEY (`m_id`)
);

CREATE TABLE `schools` (
  `s_id` int NOT NULL AUTO_INCREMENT,
  `s_name` varchar(355)
);

CREATE TABLE `schools_members` (
  `sm_id` int NOT NULL AUTO_INCREMENT,
  `sm_school_id` int NOT NULL,
  `sm_member_id` int NOT NULL,
FOREIGN KEY (sm_school_id) REFERENCES schools(s_id),
FOREIGN KEY (sm_member_id) REFERENCES members(m_id)
);

I need to display all members for a selected school by a given school id ( $schoolId ). So i assume that the query will touch on schools_members and members .

I believe the logic is: select all the sm_member_id where sm_school_id = $schoolId from table schools_members and then SELECT m_name and m_email for each m_id (member id) from table members that is IN the last query result.

This is not required , but now im curious if i want to join to this result the s_name (school name) from table schools so that each member displays the name of school also?

Answer 1

You could just use a join between schools_members and members

select m.m_name, m.m_email
from schools_members sm 
inner join members m ON m.m_id = sm.sm_member_id 
where sm.sm_school_id =  Your_value 

and for school name

select m.m_name, m.m_email, s.s_name
from schools_members sm 
inner join members m ON m.m_id = sm.sm_member_id 
inner join schools s on s.s_id = sm.sm_school_id
where sm.sm_school_id =  Your_value