summing unkown values

I would like to sum totals for unknown values. Here is the design Course names are entered in separate table -- courses If the course is still being tested the course status = open This status is stored in the Course table. Each course name is unique in this table. Test information including test time is entered in a different table -- issues The issues table includes the test time and course name values. Several entries with the same course name will be made to this table I would like to sum the total time tested based on Open courses. First I would like to know how to select the correct courses from the issues database based on the course_status in the courses databases. Would the following statement work?? $query = "select issues.course_name, issues.time_tested from issues where courses.course_status = 'open'"; $result = mysql_query( $query ); Then I need to sum the time_tested fields for all courses with the same name in the issues database that were just selected as being Open. I have been looking for some code that would do something similar to this. If anyone can point me to code or has some thoughts I would appreciate.