MYSQL PHP查询将数据从一个表获取到另一个表

Question

I need to filter data based on one table, but i dont know the correct usage for the select from function in php mysql. The below code shows what i am trying to do, but I think you can use multiple SELECT.

$query_Student = "SELECT Project_Title, Project_Lecturer FROM projects WHERE Project_id = 
 (SELECT Proj_id FROM project_course WHERE Cour_id = (SELECT Course_id from courses WHERE     
Code = (SELECT Course FROM users WHERE Username = ".$_SESSION['MM_Username']."))"

Can anyone offer any assistance to what I need to write instead?

Answer 1

What you want to do is not exactly clear to me, but to make your query work you need to put single quotes around $_SESSION['MM_Username'], like gogowitsch already said.

Also another closing paranthese is missing. So your query should look like this:

$query_Student = "SELECT Project_Title, Project_Lecturer FROM projects WHERE Project_id = 
 (SELECT Proj_id FROM project_course WHERE Cour_id = (SELECT Course_id from courses WHERE     
Code = (SELECT Course FROM users WHERE Username = '".$_SESSION['MM_Username']."')))"

But...

That is not a very well written query.

I'm just guessing now, but maybe this is what you are looking for:

SELECT 
p.Project_Title, 
p.Project_Lecturer 
FROM projects p
INNER JOIN project_course pc ON p.Project_id = pc.Proj_id
INNER JOIN courses c ON pc.Cour_id = c.Course_id
INNER JOIN users u ON c.Code = u.Course
WHERE u.Username = 'yourUserName';

If not, show us the tables you are using (do a SHOW CREATE TABLE projects; and so on for every table you are using and post it here) and maybe what output you expect, then we can really help.