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This query differs from the previous one as follows:
:The student table is added to the FROM clause because it is used in addition to the event and score tables.
:The student_id column was unambiguous before, so it was possible to refer to it in either unqualified (student_id) or qualified (score.student_id) form. Now it is ambiguous because it is present in both the score and student tables, so it must be qualified as score.student_id or student.student_id to make it clear which table to use.
:The WHERE clause has an additional term specifying that score table records are matched against student table records based on student ID:
WHERE ... score.student_id = student.student_id
:The query displays the student name rather than the student ID. (You could display both if you wanted to, of course.)
With this query, you can plug in any date and get back the scores for that date, complete with student names and the score type. You don't have to know anything about student IDs or event IDs. MySQL takes care of figuring out the relevant ID values and using them to match up table rows automatically.
Another task the grade-keeping project involves is summarizing student absences. Absences are recorded by student ID and date in the absence table. To get student names (not just IDs), we need to join the absence table to the student table, based on the student_id value. The following query lists student ID number and name along with a count of absences:
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