Question

I have tables like these two

test_table
date        student     test
2012-05-31  Alice       Math
2012-05-31  Alice       Math
2012-05-31  Bob         Math
2012-05-31  Bob         Spelling
2012-06-01  Alice       Math
2012-06-01  Alice       Spelling

score_table
date        student     test        best_daily_score
2012-05-31  Alice       Math        90
2012-05-31  Bob         Math        50
2012-05-31  Bob         Spelling    50
2012-06-01  Alice       Math        95

I’d like to detect that Alice’s best_daily_score for the Spelling test on 2012-06-01 hasn’t been recorded yet. I’m looking for the query that returns

2012-06-01  Alice       Spelling

which is the only row of

SELECT DISTINCT date, student, test FROM test_table

that is not in

SELECT DISTINCT date, student, test FROM score_table

This doesn’t work:

SELECT DISTINCT date, student, test FROM test_table WHERE date, student, test NOT IN (SELECT DISTINCT date, student, test FROM score_table)

I assume because the left side of NOT IN should not be a list of three things.

Answer 1

Give this a try:

SELECT  a.date,
        a.student,
        a.test
  FROM  test_table a 
          LEFT JOIN score_table b
            ON (a.date = b.date) AND
               (a.student = b.student) AND
               (a.test = b.test)
WHERE   b.best_daily_score IS NULL

The query tries to match all the records from test_table to score_table whether it exists or not because of the LEFT JOIN. It matches for date, student, and test. If the record was not found on score_table, so basically best_daily_score would be NULL. That’s why I added a condition to show only NULL on best_daily_score.

Click Here for some DEMO (SQLFiddle)