Issue with JOIN command - sql

Question

Hi New comer to Stack overflow so if I do not present this correctly I am sorry.
I have used Google, W3schools and read the FQA on SQL.
I am running SQL using the SQL command line in WAMP2.0. I am currently doing a project where the aim is to create a min University DB. With students, grades, programmes, modules ect
One of the tasks is to to list all the students, there modules and there correspoding grades. To do this I am trying to use a JOIN command to select all the names from the Students table, with all there corresponding modules + grades from the records table.
+------------+-------+------------+-----------------+
| Student_id | Name | DOB | Address |
+------------+-------+------------+-----------------+
| 4665236 | Paddy | 1985-09-18 | 123 Fake Street |
| 5665236 | Paul | 1984-06-12 | Good manlane |
| 6665236 | John | 1984-03-09 | Docotor town |
| 7665236 | Aidan | 1983-07-09 | Banker worlds |
| 8665236 | Joe | 1983-07-09 | 24 hitherwood |
+------------+-------+------------+-----------------+
+------------+--------+------+-------+
| Student_id | Mod_id | GPA | Grade |
+------------+--------+------+-------+
| 4655236 | 2222 | 3.84 | A- |
| 5655236 | 11111 | 3.44 | B+ |
| 6655236 | 33333 | 3.24 | B |
| 7655236 | 44444 | 2.45 | C- |
| 8655236 | 44444 | 2.45 | C- |
+------------+--------+------+-------+
The PRIMARY KEY in the students table is Student_id INT 11
The PRIMARY KEY for records is (Student_id,Mod_id)
Individual SELECT FROM , statements work fine on both tables.
Issue occurs when I use
SELECT students.Name, records.Grade
FROM students
INNER JOIN records
ON students.Student_id=Student_id
ORDER BY students.Name
I get the following error
ERROR 1052 (23000): Column 'Student_id' in on clause is ambiguous
Thanks for amazingly fast response I tried
SELECT students.Name, records.Grade
FROM students
INNER JOIN records
ON students.Student_id=records.Student_id
ORDER BY students.Name;
And Got ---- Empty set (0.00 sec) ?

Answer 1

You have to qualify that column Student_Id with an alias, something like records.studentId so that it will be un ambiguous in the ON clause, or:
SELECT s.Name, r.Grade
FROM students AS s
INNER JOIN records AS r ON s.Student_id= r.Student_id
ORDER BY s.Name

Answer 2

You need to supply the table name for column Student_id to avoid ambiguity because it both exist on the two tables.
SELECT students.Name, records.Grade
FROM students
INNER JOIN records
ON students.Student_id = records.Student_id -- << THIS
ORDER BY students.Name

Answer 3

The reason you're column name is being flagged as ambiguous is because you've got two different tables that each have the Student_id field. You can join a table to itself, so even though you've got an identifier on the first instance of the field you need one on both.
Try the following code:
SELECT students.Name, records.Grade
FROM students
INNER JOIN records
ON students.Student_id=records.Student_id
ORDER BY students.Name
You can also alias the tables if that helps your code look cleaner by using the following:
SELECT s.Name, r.Grade
FROM students s
INNER JOIN records r
ON s.Student_id=r.Student_id
ORDER BY s.Name
However, this only works if the Student IDs match in both tables. in the example data you've presented there are no matching records. 4665236 != 4655236