Below is the list of tables from the database along with their columns and datatype. Need to generate an accurate SQL query for the question.
Only use the columns present in the respective table. Only use the columns which are required to generate the SQL query. Only use table joins if required and not otherwise.

### Tables ###
TABLE: CREATE TABLE students ( student_id VARCHAR )
TABLE: CREATE TABLE student_course_registrations ( student_id VARCHAR )

### Question ###
List the id of students who registered some courses and the number of their registered courses?

### Accurate SQL ###

SELECT T1.student_id, COUNT(*) FROM students AS T1 JOIN student_course_registrations AS T2 ON T1.student_id = T2.student_id GROUP BY T1.student_id