Q.5 In SQL, foreign key constraints can only reference the primary key attributes of the referenced relation, or other attributes declared to be a super key using the unique constraint. As a result, total participation constraints on a many-to-many relationship (or on the "one" side of a one-to-many relationship) cannot be enforced on the relations created from the relationship, using primary key, foreign key and not null constraints on the relations. a. Explain the reason. b. Explain how

Q.5 In SQL, foreign key constraints can only reference the primary key attributes of the referenced relation, or other attributes declared to be a super key using the unique constraint. As a result, total participation constraints on a many-to-many relationship (or on the "one" side of a one-to-many relationship) cannot be enforced on the relations created from the relationship, using primary key, foreign key and not null constraints on the relations. a. Explain the reason. b. Explain how

Database Systems: Design, Implementation, & Management

12th Edition

ISBN:9781305627482

Author:Carlos Coronel, Steven Morris

Publisher:Carlos Coronel, Steven Morris

Chapter8: Advanced Sql

Section: Chapter Questions

Problem 18RQ

See similar textbooks

Similar questions

In SQL, foreign key constraints can reference only the primary key attributes ofthe referenced relation or other attributes declared to be a superkey using theunique constraint. As a result, total participation constraints on a many-to-manyrelationship set (or on the “one” side of a one-to-many relationship set) cannotbe enforced on the relations created from the relationship set, using primarykey, foreign key, and not null constraints on the relations. Explain how to enforce total participation constraints using complexcheck constraints or assertions (see Section 4.4.8). (Unfortunately, thesefeatures are not supported on any widely used database currently.)
So SQL does not suppor functional depency constraints. However, if the database system supports constraints on materialized views and materialized views are maintained immediately, is it possible to enforce the functional dependency constraints in SQL? If it is possible, for a relation r(A,B,C), how can the constraints on materialized views be used to enforce a functional dependency, like B->A?
In SQL, foreign key constraints can reference only the primary key attributes ofthe referenced relation or other attributes declared to be a superkey using theunique constraint. As a result, total participation constraints on a many-to-manyrelationship set (or on the “one” side of a one-to-many relationship set) cannotbe enforced on the relations created from the relationship set, using primarykey, foreign key, and not null constraints on the relations. Explain why
Consider a many-to-one relationship R between entity sets A and B. Supposethe relation created from R is combined with the relation created from A. InSQL, attributes participating in a foreign key constraint can be null. Explainhow a constraint on total participation of A in R can be enforced using not nullconstraints in SQL.
Please answer this DBMS ques asap! Suppose that we have three relations R1={A, B, C}, R2={A, B, D} and R3={B, C, D} under the relational data model. The relation R1 has 5 tuples, the relation R2 has 6 tuples and the relation R3 has 7 tuples. There are no NULL values in these relations. For each of the following relational algebra expressions, list the minimum and maximum numbers of tuples in the result that the relational algebra expression may have. (1) πA,B(R1)(2) R2 × πB(R3)(3) πB(R2) ∪ πB(R3)(4) R1 ⋈ R2(5) ρX (R2) ⋈X.B≠Y.B ρY (R2) You can use the following format to organise your answers.(1) max=____ , min=____ ;(2) max=____ , min=____ ;(3) max=____ , min=____ ;(4) max=____ , min=____ ;(5) max=____ , min=____ ;
Q7. Consider a database containing two relations: R(A,B,C) and S(D,E,F). For each of three (your choice) of the 12 rewriting rules for relational algebra expression, give an example pair of relational algebra expressions involving R and S such that the rule rewrites one expression to the other expression, and give another example pair to show the rewriting rule cannot be used since some of the conditions for the rule are not satisfied.
Consider the following SQL query on the university schema: select avg(salary)-(sum(salary) / count(*)) from instructorWe might expect that the result of this query is zero since the average of a set of numbers is defined to be the sum of the numbers divided by the number of numbers. Indeed this is true for the example instructor relation in Figure 2.1. However, there are other possible instances of that relation for which the result would not be zero. Give one such instance, and explain why the result would not be zero.
Database Systems For each part of this problem you will need to construct a single SQL query which will check whether a certain condition holds on a specific instance of a relation, in the following way: your query should return an empty result if and only if the condition holds on the instance. (If the condition doesn’t hold, your query should return something non-empty). Note our language here: the conditions that we specify cannot be proved to hold in general without knowing the externally-defined functional dependencies; so what we mean is, check whether they could hold in general for the relation, given a specific set of tuples. You may assume that there will be no NULL values in the tables, and you may assume that the relations are sets rather than multisets, but otherwise your query should work for general in- stances. A is a superkey for a relation T (A, B, C, D). The combinations of two attributes in the relation T (A, B, C, D) are each keys. A tuple-generating…
Consider the relational schemas given below and the respective sets of functional dependencies valid in the schemas. C(A,B,C,D,E,F,G,H) ?????????? ??????????: C,H > G A>BC B > CFH D > A F > EG (i) Find all the minimal super keys of the relational table ?. List the derivations of all minimal keys.(ii) Identify the highest normal form of the relational table ?. Remember that the identification of a normal form requires analysis of the valid functional dependencies.(iii) Decompose the relational table ? into minimal number of normalized relational tables in BCNF. Remember to indicate the primary key and foreign keys (if any).
Consider the relation r(A, B, C) with the attribute A as the index. Give an example of a query that can be answered only by looking at the index, rather than the tuples in the relationship. (Index-only plans are query plans that just utilise the index and do not access the actual relation.)
Give an SQL schema definition for the employee database of Figure 3.19.Choose an appropriate domain for each attribute and an appropriate primarykey for each relation schema. Include any foreign-key constraints that might beappropriate.
Transform the diagram to a relational schema that shows referential integrity constraints (see the following figure for an example of such a schema – underlined items are primary keys, dotted underlines refer to foreign keys, while the arrows indicate direction from foreign to primary)