Database, Relational Algebra, Relational Calculus, SQL Assertions Please show th

Question

Database, Relational Algebra, Relational Calculus, SQL Assertions

Please show the derivation of each of the answers if possible. Thanks in advance.

Problenm In this problem you will express a referential integrity constraint using a general SQL assertion. Assume that there are two tables R (A) and S (A). Using a general SQL assertion, express that s . A s a foreign key referencing R . A. That is, there should not be any S.A value that does not appear in R.A. Note that a general SQL assertion is not attached to a particular table. Therefore, whenever a SQL modification statement is executed that may potentially violate the assertion, the DBMS checks the result of the statement and rejects the statement if it causes violation. This behavior is the same as the default semantics of a foreign-key constraint Complete what I started here: CREATE ASSERTION FKey (NOT (SELECT* FROM S WHERE A (SELECT A FROM R))) Problenm Consider the table R (A, B), which currently has only one tuple (1,0). Assume that the following trigger has already been created for the database CREATE TRIGGER Times2 AFTER UPDATE ON R REFERENCING NEW ROW AS n FOR EACH ROW WHEN (n.B

Explanation / Answer

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1)

CREATE ASSERTION FKey CHECK (NOT EXISTS(
    SELECT *
    FROM S
    WHERE A NOT IN (SELECT A
        FROM R)));

2)

SELECT * FROM R;

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