I am trying to figure out how I can use aggregate functions to solve this problem. For example if I had the table

enrolled(student-id, course-id)
123 897
123 645
589 452
009 897

If I wanted to find the number of courses each student is enrolled in, how would I go about doing that? I was thinking of using the count function but I don't know how to separate each student-id


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  • $\begingroup$ You could use the group by operator. $\endgroup$ – Renzo Feb 13 at 15:33

Use the GROUP BY and COUNT operators.

  • $\begingroup$ just to clarify, is this in SQL or relational algebra? $\endgroup$ – temp948 Feb 13 at 17:43
  • $\begingroup$ @temp948, this is SQL. $\endgroup$ – D.W. Feb 13 at 19:38
  • $\begingroup$ i am talking about relational algebra here, not sql. $\endgroup$ – temp948 Feb 15 at 14:25
  • $\begingroup$ @temp948, perhaps you could edit the question to state that in the question? $\endgroup$ – D.W. Feb 15 at 17:56

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