List two reasons why null values might be introduced into the database.
Answer to relevant QuestionsCertain systems allow marked nulls. A marked null ⊥i is equal to itself, but if i ≠ j, then ⊥i ≠ ⊥j. One application of marked nulls is to allow certain updates through views. Consider the view ...Let R = (A, B, C), and let r1 and r2 both be relations on schema R. Give an expression in SQL that is equivalent to each of the following queries. a. r1 ∪ r2 b. r1 ∩ r2 c. r1 − r2 d. II AB(r1) 1 ...SQL-92 provides an n-ary operation called coalesce, which is defined as follows: coalesce (A1,A2, . . . , An) returns the first nonnull Ai in the list A1,A2, . . .,An, and returns null if all of A1,A2, . . .,An are null. ...Consider the relational database of Figure. Give expressions in QBE for each of the following queries:a. Modify the database so that Jones now lives in Newtown.b. Give all employees of First Bank Corporation a 10 percent ...Referential-integrity constraints as defined in this chapter involve exactly two relations. Consider a database that includes the following relations:salaried-worker (name, office, phone, salary)hourly-worker (name, ...
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