Primary key, PL-SQL Programming

PRIMARY KEY:

PRIMARY KEY  indicates that the table is subject to a key constraint, in this case declaring that no two rows in the table assigned to ENROLMENT can ever have the same combination of StudentId and CourseId fields (i.e., we cannot enrol the same student on the same course more than once, so to speak). We will learn more about SQL constraints in general and SQL's key constraints.

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