DBI202 - Part 6
All of the others
3NFconcept is related to (choose 1 answer only): a. Atomic definition b. Full dependency definition c. Transitive dependency definition d. Super Key definition
data model
A ___ is a notation for describing the structure of the data in a database, along with the constraints on that data
DBMS
A ____ is a powerful tool for creating and managing large amounts of data efficiently and allowing it to persist over long periods of time, safely
Nested
A ____ table is a table that is embedded within another table
Collation
A _____ specifies which characters are "less than" which other characters
semi-structured
A database of _____ data model is a collection of nodes, each node is either a leaf or interior
"Consistent" means that: Transactions must not violate any integrity constraints during its execution
A database transaction, by definition, must be ACID (atomic, consistent, isolated and durable). What does "Consistent" mean?
"Isolated" means that: how/when the changes made by one operation in one transaction become visible to other concurrent operations in other transactions
A database transaction, by definition, must be ACID (atomic, consistent, isolated and durable). What does "Isolated" mean?
have either a matching value in the referring (primary) table OR be NULL
A foreign key must
Comparisons between two null values, or between a NULL and any other value, return unknown
Choose one correct statement:
In SQL Server, every DML operation is a transaction regardless of whether it has a BEGIN TRANSACTION or not
Choose the in-correct statement:
All of the others
Choose the most correct statement. Database is created and maintained by a DMBS Database is a collection of data that is managed by a DBMS Database is a collection of information that exists over a long period of time
20
Column A of a relation has the following list of values in the six rows of the table: NULL, NULL, 10, 10, 20, 30 In SQL Server, which of the following is the correct value of AVG(DISTINCT A)?
H has a tuple (3, 5)
Consider the Datalog rule H(x,y) <- S(x, y) AND x > 2 AND y < 6. Relation S(x, y) has 3 tuples (2, 3), (3, 5), and (4, 6). What is about H?
False
Consider the law, that holds for set relations: T intersect(R union S) = (T intersect R) union (T intersect S) The above law still hold for bag relations?
False b
Consider the law, that holds for set relations:(S intersect T) - R = S intersect (T - R).The above law still hold for bag relations?
"_" represents exactly 1 character
Pay attention to the following query:SELECT * FROM R WHERE A LIKE '%_%'; So, in the above case, the wildcard "_" represents what?
We should decompose relation to eliminate anomalies
How to eliminate anomalies when we design a database?
binary relationship
In UML, a _____ between classes is called an association
In composition, when the owning object is destroyed, so are the contained objects. In aggregation, this is not necessarily true.
In UML, what is the difference between an aggregation and a composition?
R is in 2NF
Let R(A,B,C,D) with the following FDs: {AB->C, AC->B, AD->C} Choose a correct statement about R:
(a) and (b) are correct
Look at the following statements:(a)We should pick the right kind of elements (b) When an entity has no non-primary key attribute, we should convert that entity to an attribute (c) Use weak entities when-ever possible (d) Always make redundancies
4
Suppose R is a relation with attributes A1, A2, A3, A4. The only key of R is {A1, A2}. So, how many super-keys do R have?
Selects all customers from table Sales that have made more than 5 orders.
Suppose relation R(a,b,c) has the following tuples: Which tuple is contained in the result of the following query:
w <= x+y
Suppose that tuple t appears, respectively, x, y, and z times in the relations X, Y, and Z. Let t appear w times in the relation: X union (Y intersect Z).Which of the following inequalities is true ?
6
Suppose the relation S(B,C,D) has tuples:Compute the result of the following query: SELECT SUM(D) FROM S WHERE D < 8 AND D > 5
Determines if a value matches any of the values in a list or a sub-query
The IN SQL keyword
Specifies a range to test.
The SQL BETWEEN operator:
a. (a) and (c) are true
The benefits of stored procedures are: (a)They improve the security by letting the admin to LIMIT the access rights of users (b) They can save a lot of storage space (c) They can be reused many times (d) They can store a part of the database in order to retrieve the data more quickly
Association
The binary relationship between classes in UML is called ...
R is in 3NF
The relation R(ABCD) has following FDs: {ACD -> B ; AC -> D ; D -> C ; AC -> B} Choose the correct statement about R:
(4,4)
The table Arc(x,y) currently has the following tuples (note there are duplicates): SELECT x, COUNT(y)FROM Arc GROUP BY x; Which of the following tuples is in the result?
There is an error
The table R(X,Y) currently has the following tuples (note there are duplicates).The relation S(A,B,C) has the following tuples: Which is the result when we execute the following query:
ALTER TABLE
To update a relation's schema, which one of the following statements can be used?
Indexes
Well-designed ____ can reduce disk I/O operations and consume fewer system resources therefore improving query performance
'join' used to connect two or more tables logically with or without common field(s)
What is a "join"?
A key attribute is an attribute that belongs to one of the keys of the relation
What is a key attribute in a relation?
A table can have more than one UNIQUE KEY constraint but only one PRIMARY KEY
What is difference between PRIMARY KEY and UNIQUE KEY ?
A hierarchical data model is a data model in which the data is organized into a tree-like structure
What is the hierarchical data model?
All of the others c
When we apply set operators (UNION, INTERSECT, EXCEPT) to two relations R and S, which conditions on R and S must be satisfied? a. R and S must have schemas with identical sets of attributes and the types (domains) for each attributes must be the same in R and S b. Before we compute the set-theoretic union, intersection, or difference of sets of tuples, the columns of R and S must be ordered so that the order of attributes is the same for both relations
For any relation schema, there is a dependency-preserving decomposition into 3NF
Which of the following statements is correct?
d. All of the others
Which of the following statements is the most correct? a. Using Stored procedures reduces network traffic b. Using Stored procedures improves security c. Using Stored procedures improves performance
All of the others. d
Which of the following statements is true? a. BCNF condition guarantees the non existence of the anomalies. b. In BCNF condition, the left side of every non trivial FD must be a super key. c. Any two-attribute relation is in BCNF.
ALTER TABLE
Which one of the following is NOT a DML command?
Because the intersection operator can be expressed through the union operator and the difference operator
Why the intersection operator is not called a primitive relational algebra operator?