Data Management (Foundations) D426
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Free Data Management (Foundations) D426 Questions
What is the term for a key that consists of a single attribute and is used to uniquely identify a record in a database table?
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Unique key
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Simple primary key
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Candidate key
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Surrogate key
Explanation
Correct Answer:
Simple primary key
Explanation:
A simple primary key is a primary key that consists of only one attribute (column) used to uniquely identify each record in a table. This is in contrast to a composite key, which requires multiple attributes. A simple primary key is straightforward, easy to manage, and ensures entity integrity by enforcing uniqueness and non-null constraints on that single column.
Why Other Options Are Wrong:
Unique key
A unique key enforces uniqueness of values in a column, but unlike a primary key, it can allow null values (in most systems). It also is not specifically defined as the primary identifier of a record.
Candidate key
A candidate key is any attribute or combination of attributes that could serve as a primary key. While a simple primary key is one type of candidate key, the term candidate key itself does not specifically indicate that it has been chosen as the actual primary key.
Surrogate key
A surrogate key is an artificially created key, usually an auto-incremented number, used when no natural attribute uniquely identifies records. It is not necessarily simple in the sense of being a natural single attribute like a simple primary key.
Tables in Boyce-Codd Normal Form (BCNF) if the table is in 3NF and ________.
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data integrity is enforced
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no hidden dependencies exist between non-key fields and key fields
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referential integrity is enforced
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the table is indexed
Explanation
Correct Answer
B. no hidden dependencies exist between non-key fields and key fields
Explanation
Boyce-Codd Normal Form (BCNF) is a stricter version of the Third Normal Form (3NF). A table is in BCNF if, for every functional dependency, the left-hand side is a superkey. This means there must be no hidden dependencies between non-key attributes and key attributes, which ensures that the table is in BCNF.
Why other options are wrong
A. data integrity is enforced
Data integrity is important for all normal forms, but it is not the defining characteristic of BCNF. BCNF specifically addresses functional dependencies and key structures.
C. referential integrity is enforced
Referential integrity ensures that relationships between tables are maintained through foreign keys, but this is not the defining characteristic of BCNF. BCNF focuses on the structure of dependencies within a single table.
D. the table is indexed
Indexes are related to performance, not normal form. While indexing may improve query performance, it is not a requirement for a table to be in BCNF.
Which SQL statement ADDS UPDATE PRIVILEGE to a ROLE manager on salary table?
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ADD UPDATE PRIVILEGE TO MANAGER
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GRANT UPDATE ON salary TO manager
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UPDATE salary BY manager
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SET UPDATE PRIVILEGE ON salary TO manager
Explanation
Correct Answer:
GRANT UPDATE ON salary TO manager
Explanation:
In SQL, privileges such as SELECT, INSERT, UPDATE, or DELETE are granted to users or roles using the GRANT command. The correct syntax to provide update privileges on a specific table to a role is "GRANT UPDATE ON [table] TO [role]." Therefore, "GRANT UPDATE ON salary TO manager" correctly adds the UPDATE privilege to the role named manager for the salary table. This follows SQL standards and ensures the role can update rows in that table.
Why Other Options Are Wrong:
ADD UPDATE PRIVILEGE TO MANAGER
This syntax is invalid in SQL. There is no "ADD PRIVILEGE" statement in standard SQL. Privileges must be given using the GRANT statement, making this option incorrect.
UPDATE salary BY manager
This looks like a modification statement, but it is syntactically incorrect. UPDATE in SQL modifies data within a table and does not control permissions. It cannot be used to assign privileges to a role.
SET UPDATE PRIVILEGE ON salary TO manager
The word "SET" is not used in SQL for permissions. SET is used to assign variables or configuration parameters, not privileges. This statement is not valid SQL syntax for managing access control.
Without comparing columns, what kind of join joins two tables?
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SELF
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EQUIJOIN
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OUTER
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CROSS
Explanation
Correct Answer
D. CROSS
Explanation
A CROSS JOIN combines every row from the first table with every row from the second table, resulting in a Cartesian product. No conditions are applied to compare columns in this type of join. The number of rows in the result set is the product of the number of rows in both tables.
Why other options are wrong
A. SELF
This is incorrect because a SELF JOIN is a join of a table with itself, and it typically requires a condition to compare the table to itself.
B. EQUIJOIN
This is incorrect because an EQUIJOIN is a join based on matching column values between two tables. It compares columns to find matching values.
C. OUTER
This is incorrect because an OUTER JOIN (LEFT, RIGHT, or FULL) compares columns between two tables to include rows that have matching values or null values from either table. It is based on comparison, not simply a combination of rows.
Hash index entries are assigned to _____:
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clusters
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values
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blocks
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buckets
Explanation
Correct Answer
D. buckets
Explanation
Hash indexes use a hashing function to assign index entries to "buckets." Each bucket stores a group of entries that have the same hash value. This allows for efficient lookup and retrieval of data based on the hash of the key. Hashing ensures that data is evenly distributed across these buckets, which helps speed up the indexing process.
Why other options are wrong
A. clusters
Clusters refer to a storage organization technique in which related data is stored together physically. It is not directly related to the assignment of hash index entries.
B. values
Hash index entries are not assigned to specific values; they are assigned to buckets. The hash function maps values to buckets, not directly to the values themselves.
C. blocks
Blocks refer to units of storage in a database. While data is stored in blocks, hash index entries are specifically assigned to buckets, not blocks.
What is the significance of cardinality in an entity-relationship diagram (ER diagram) when interpreting the relationship between entities?
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It indicates the type of data stored in each entity.
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It defines the number of instances of one entity that can or must be associated with each instance of another entity.
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It represents the primary key of an entity.
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It shows the order of operations in a database query.
Explanation
Correct Answer:
It defines the number of instances of one entity that can or must be associated with each instance of another entity.
Explanation:
Cardinality in an ER diagram describes the numerical relationship between entities, such as one-to-one, one-to-many, or many-to-many. It determines how many instances of one entity correspond to instances of another, ensuring clarity in database design. For example, one department may have many employees, but each employee belongs to only one department. This makes cardinality critical for understanding and enforcing relational constraints.
Why Other Options Are Wrong:
It indicates the type of data stored in each entity.
This refers to data types (like integer, text, or date), which are not defined by cardinality but by attributes in the schema.
It represents the primary key of an entity.
Primary keys uniquely identify rows within a table, but they are not related to cardinality. Keys ensure entity integrity, while cardinality defines relationships.
It shows the order of operations in a database query.
This relates to query execution and optimization, not ER modeling. Cardinality is about entity relationships, not query processing order.
The order of precedence for the logical operators in a WHERE clause is
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Not, And, Or
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And, Or, Not
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Or, And, Not
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Not, Or, And
Explanation
Correct Answer
A. Not, And, Or
Explanation
In SQL, the order of precedence for logical operators in a WHERE clause is:
NOT (highest precedence)
AND
OR (lowest precedence)
This means that NOT is evaluated first, followed by AND, and finally, OR. This is important when you are using multiple logical operators in a query because it ensures that the operations are performed in the correct order.
Why other options are wrong
B. And, Or, Not
This is incorrect because NOT has higher precedence than both AND and OR.
C. Or, And, Not
This is incorrect because OR has the lowest precedence, not the highest.
D. Not, Or, And
This is incorrect because OR has a lower precedence than AND.
What is the initial step required in the process of defining supertype and subtype entities in database design?
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Establish relationships
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Identify entities
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Define attributes
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Determine constraints
Explanation
Correct Answer
B. Identify entities
Explanation
The first step in defining supertype and subtype entities in database design is to identify the entities that will serve as supertypes and subtypes. Identifying entities allows the designer to determine which entities share common attributes and which entities will inherit specific characteristics from a parent (supertype) entity.
Why other options are wrong
A. Establish relationships
Establishing relationships comes after identifying entities. Once the supertypes and subtypes are identified, relationships can be established to define how they interact.
C. Define attributes
Defining attributes occurs after identifying the entities. The attributes will be defined based on the entities, but the first step is identifying the entities themselves.
D. Determine constraints
Determining constraints, such as primary keys or foreign keys, comes after the entities and their relationships have been defined. Constraints are essential for data integrity, but they are not the first step in the process.
In the case of entity integrity, the primary key may be
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Not Null
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Null
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Both Null & Not Null
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Any value
Explanation
Correct Answer:
Not Null
Explanation:
Entity integrity is a fundamental rule in relational databases stating that every table must have a primary key and that the primary key must contain unique, non-null values. A primary key uniquely identifies each record, and allowing null values would break this rule because null indicates "unknown" and cannot serve as a reliable identifier. Therefore, a primary key must always be defined as NOT NULL to maintain entity integrity.
Why Other Options Are Wrong:
Null
A primary key cannot be null because null means no value or unknown, making it impossible to identify a record uniquely. If allowed, multiple rows could have null in the primary key, violating entity integrity.
Both Null & Not Null
This is incorrect because a primary key must consistently follow the NOT NULL rule. Having some rows null and others not null would defeat the purpose of uniquely identifying records and would violate relational database design principles.
Any value
Allowing any value implies including nulls or duplicates, both of which are forbidden for primary keys. A primary key must always hold unique and not null values to ensure proper identification of rows.
Which of the following functions is classified as an aggregation function in SQL?
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COUNT
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UPPER
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LEFT
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CHAR_LENGTH
Explanation
Correct Answer:
COUNT
Explanation:
COUNT is an aggregate function in SQL used to return the number of rows that match a specified condition. It summarizes data by providing totals over sets of rows, which is the purpose of aggregation functions. Aggregates like COUNT, SUM, AVG, MAX, and MIN are applied in GROUP BY queries to analyze collections of data, making COUNT the correct answer here.
Why Other Options Are Wrong:
UPPER
UPPER is a string function that converts text to uppercase. It operates on individual string values, not groups of rows, so it is not an aggregate function.
LEFT
LEFT is a string function used to extract a certain number of characters from the left side of a string. Like UPPER, it acts on single values and is not meant to summarize sets of rows.
CHAR_LENGTH
CHAR_LENGTH returns the number of characters in a string. This function evaluates string length for each individual value, not across multiple rows, so it is not an aggregate function.
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