refs #249, improve sql statement

db/migrations/1.310_add_seminare_semester_table.php

@@ -29,11 +29,10 @@ class AddSeminareSemesterTable extends Migration
             FROM `seminare`
             INNER JOIN `semester_data` ON (`seminare`.`start_time` < `semester_data`.`ende`
                      AND (
-                         (`seminare`.`start_time` >= `semester_data`.`beginn` AND `seminare`.`duration_time` = '0')
-                         OR (`seminare`.`duration_time` > 0 AND `seminare`.`start_time` + `seminare`.`duration_time` >= `semester_data`.`beginn`)
+                         `seminare`.`start_time` >= `semester_data`.`beginn` AND `seminare`.`duration_time` >= '0'
                      )
-                )"
-        );
+                )
+        ");
     }
 
     public function down()