Joining Two MYSQL tables

Question

SOLVED: I forgot to select for a certain value so the query was just returning the first grade it found.

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I have 2 tables and I would like to combine part of one and part of the other

The first table, Grades, has
COURSE_NUMBER , SECTION_NUMBER , GRADE_A , GRADE_B GRADE_C

The second table, Sections, has
COURSE_NUMBER , SECTION_NUMBER , INSTRUCTOR

I would like to output the results so I can see

COURSE NUMBER | SECTION NUMBER | INSTRUCTOR | GRADE A | GRADE B | GRADE C

I've tried using JOIN and i'm getting the correct course and section number with the correct instructor. However the grades are not matching up with the course and section number from the first table.

Heres the query that gets me the incorrect grades

SELECT Grades.COURSE_NUMBER, Grades.SECTION_NUMBER, Sections.INSTRUCTOR,     
Grades.A, Grades.B, Grades.C 
FROM `Grades` INNER JOIN `Sections` on Grades.COURSE_NUMBER = Sections.COURSE 
and Grades.SECTION_NUMBER = Sections.SECTION 

I don't have a lot of experience with databases so any suggestions on simplifying this problem are also appreciated.

Thank you

EDIT:

Sample data for the Grades table:

|  Course_number    |  Section_number   | A | B | C |
|       101         |        001        | 4 | 1 | 0 |
|       101         |        002        | 5 | 2 | 8 |
|       102         |        001        | 7 | 9 | 4 |

Sample data for the Section table:

|  Course_number    |  Section_number   |  Instructor  |
|       101         |        001        |     Alex     |
|       101         |        002        |     Jeff     |
|       102         |        001        |     Greg     |

Expected Result:

| COURSE NUMBER | SECTION NUMBER | INSTRUCTOR | GRADE A | GRADE B | GRADE C |
|      101      |       001      |    Alex    |    4    |    1    |    0    |
|      101      |       002      |    Jeff    |    5    |    2    |    8    |
|      102      |       001      |    Greg    |    7    |    9    |    4    |

Not-working Result:

| COURSE NUMBER | SECTION NUMBER | INSTRUCTOR | GRADE A | GRADE B | GRADE C |
|      101      |       001      |    Alex    |    25   |    9    |    2    |
|      101      |       002      |    Jeff    |    0    |    34   |    6    |
|      102      |       001      |    Greg    |    2    |    3    |    12   |

(The grades are just being randomly pulled from somewhere in the Grades table, its very large)

Answer 1

Your query seems conceptually right, but there is a difference between the column names you use and those you describe in your tables structure.

Try changing it this way

SELECT  t1.COURSE_NUMBER,
        t1.SECTION_NUMBER,
        t2.INSTRUCTOR,     
        t1.GRADE_A, t1.GRADE_B, t1.GRADE_C 
FROM    Grades t1
INNER JOIN
        Sections t2
ON      t1.COURSE_NUMBER = t2.COURSE_NUMBER AND
        t1.SECTION_NUMBER = t2.SECTION_NUMBER

I added aliases to the tables to make it more compact, but obviously feel free to switch back to full tables names if you prefer.

Answer 2

SELECT Grades.COURSE_NUMBER, Grades.SECTION_NUMBER,Sections.INSTRUCTOR,Grades.A, Grades.B, Grades.C
FROM Grades,Sections
WHERE Grades.COURSE_NUMBER = Sections.COURSE_NUMBER 
AND Grades.SECTION_NUMBER = Sections.SECTION_NUMBER

Answer 3

Please try this.

SELECT Grades.COURSE_NUMBER, 
Grades.SECTION_NUMBER,Sections.INSTRUCTOR,Grades.A, 
Grades.B, Grades.C
FROM Grades,Sections
WHERE Grades.COURSE_NUMBER = Sections.COURSE 
AND Grades.SECTION_NUMBER = Sections.SECTION