BCS 260 Lecture Notes - Lecture 3: Foreign Key, Unique Key, Referential Integrity

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1 Jul 2022
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This means: the field i refer to is a primary key in the other table (student, the values in this column must exist in the other table (student) A foreign key is a column or group of columns in a relational database table that provides a link between data in two tables. It acts as a cross-reference between tables because it references the primary key of another table, thereby establishing a link database between them. Recall the test for a superkey: it uniquely identifies every tuple currently in the database and, we cannot conceive of adding tuples where this row is duplicated. The foreign key is a superkey only in the foreign relation not this relation. Composite of year, courseid and ram (you can"t register for the same class twice in the same semester) Maintaining integrity of relationships in tables (deleting records in one table, should related records be deleted in another table)

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