Question

I have the following database tables and columns:

students
+------------+-------------------+------------------+
| student_id | student_firstname | student_lastname |
+------------+-------------------+------------------+
|         95 | John              | Doe              |
+------------+-------------------+------------------+

studentcourseplan
+--------+------------+
| cpl_id | student_id |
+--------+------------+
|    209 |         95 |
|    273 |         95 |
+--------+------------+

studentdates
+------------+-------------------+-----------------+
| student_id | student_startdate | student_enddate |
+------------+-------------------+-----------------+
|         95 | 2012-07-02        | 2012-08-17      |
|         95 | 2012-08-20        | 2012-11-16      |
+------------+-------------------+-----------------+

If I run this query…

SELECT 
    scp.cpl_id,
    s.student_id,
    s.student_firstname,
    s.student_lastname,
    sd.student_startdate,
    sd.student_enddate
FROM
    studentcourseplan scp
        INNER JOIN
    students s ON s.student_id = scp.student_id
        INNER JOIN
    studentdates sd ON sd.student_id = s.student_id

… I get the following output:

+--------+------------+-------------------+------------------+-------------------+-----------------+
| cpl_id | student_id | student_firstname | student_lastname | student_startdate | student_enddate |
+--------+------------+-------------------+------------------+-------------------+-----------------+
| 209    |         95 | John              | Doe              | 2012-07-02        | 2012-08-17      |
| 273    |         95 | John              | Doe              | 2012-07-02        | 2012-08-17      |
+--------+------------+-------------------+------------------+-------------------+-----------------+

Notice the dates from result compared to the values in the table studentdates. They are wrong. I want something like the following output instead:

+--------+------------+-------------------+------------------+-------------------+-----------------+
| cpl_id | student_id | student_firstname | student_lastname | student_startdate | student_enddate |
+--------+------------+-------------------+------------------+-------------------+-----------------+
| 209    |         95 | John              | Doe              | 2012-07-02        | 2012-08-17      |
| 273    |         95 | John              | Doe              | 2012-08-20        | 2012-11-16      |
+--------+------------+-------------------+------------------+-------------------+-----------------+

What am I doing wrong?

Answer 1

You need to map cpl_id with studentdates. You can add one column to studentdates called cpl_id & then change the query accordingly.