Fix typo in SQL query.

src/main/java/nl/tudelft/ewi/tam/repositories/CourseEditionRepository.java

@@ -75,7 +75,7 @@ public class CourseEditionRepository {
      * The {@link String} instance to check whether a course with a specific id is active.
      */
     protected static final String CHECK_ACTIVE = "SELECT C.* FROM Schedule AS S LEFT JOIN CourseEdition AS C ON"
-            + " S.year = C.year AND S.quarter = C.quarter LEFT JOIN CourseDescription AS CD ON C.id = CD.c_id"
+            + " S.year = C.year AND S.quarter = C.quarter LEFT JOIN CourseDescription AS CD ON C.id = CD.ce_id"
             + " WHERE interest = 1 AND C.id = ?";
 
     /**