WGU C949 Data Structures and Algorithms I Complete
Study Guide – WGU C949 Practice Questions, Verified
Answers, Algorithm Concepts, Coding Logic, and Exam
Preparation Materials for Western Governors University
Students
Question 1: Which SQL command is used to retrieve data from a database?
A. INSERT
B. UPDATE
C. SELECT
D. DELETE
CORRECT ANSWER: C. SELECT
Rationale: The SELECT statement is the fundamental SQL command used to query and retrieve
data from one or more tables in a relational database.
Question 2: What does ACID stand for in the context of database transactions?
A. Atomicity, Consistency, Isolation, Durability
B. Accuracy, Consistency, Integrity, Durability
C. Atomicity, Clarity, Isolation, Dependency
D. Availability, Consistency, Isolation, Durability
CORRECT ANSWER: A. Atomicity, Consistency, Isolation, Durability
Rationale: ACID is a set of properties of database transactions intended to guarantee validity
even in the event of errors, power failures, etc. It stands for Atomicity, Consistency, Isolation,
and Durability.
Question 3: Which normal form eliminates transitive dependencies?
A. First Normal Form (1NF)
B. Second Normal Form (2NF)
C. Third Normal Form (3NF)
D. Boyce-Codd Normal Form (BCNF)
CORRECT ANSWER: C. Third Normal Form (3NF)
Rationale: Third Normal Form (3NF) requires that the table is in 2NF and all non-key attributes
are not transitively dependent on the primary key.
Question 4: What is the primary key in a relational database table?
A. A key that allows null values
B. A unique identifier for each record in a table
C. A key used to link two tables together
D. A key that can be duplicated across records
CORRECT ANSWER: B. A unique identifier for each record in a table
Rationale: A primary key is a specific choice of a minimal set of attributes (columns) that
uniquely specify a tuple (row) in a relation (table). It cannot contain null values.
Question 5: Which clause is used to filter records in a SQL query?
A. ORDER BY
B. GROUP BY
C. WHERE
D. HAVING
,CORRECT ANSWER: C. WHERE
Rationale: The WHERE clause is used to extract only those records that fulfill a specified
condition before any grouping occurs.
Question 6: What type of join returns all records when there is a match in either left or right
table?
A. INNER JOIN
B. LEFT JOIN
C. RIGHT JOIN
D. FULL OUTER JOIN
CORRECT ANSWER: D. FULL OUTER JOIN
Rationale: A FULL OUTER JOIN returns all records when there is a match in either the left or
right table records, filling in NULLs for missing matches.
Question 7: Which command is used to remove a table from a database?
A. DELETE TABLE
B. REMOVE TABLE
C. DROP TABLE
D. ERASE TABLE
CORRECT ANSWER: C. DROP TABLE
Rationale: The DROP TABLE command is used to delete the table structure and all data stored
within it from the database.
Question 8: What is a foreign key?
A. A key that uniquely identifies a record in another table
B. A key used to encrypt data
C. A key that allows duplicate values only
D. A key used to sort data alphabetically
CORRECT ANSWER: A. A key that uniquely identifies a record in another table
Rationale: A foreign key is a field (or collection of fields) in one table that refers to the primary
key in another table, establishing a link between the two.
Question 9: Which SQL function is used to count the number of rows?
A. SUM()
B. COUNT()
C. AVG()
D. TOTAL()
CORRECT ANSWER: B. COUNT()
Rationale: The COUNT() function returns the number of rows that matches a specified criterion.
Question 10: What is the purpose of an index in a database?
A. To secure data from unauthorized access
B. To speed up data retrieval operations
C. To store backup copies of data
D. To enforce data types
CORRECT ANSWER: B. To speed up data retrieval operations
,Rationale: An index is a data structure that improves the speed of data retrieval operations on a
database table at the cost of additional writes and storage space.
Question 11: Which constraint ensures that all values in a column are different?
A. NOT NULL
B. UNIQUE
C. DEFAULT
D. CHECK
CORRECT ANSWER: B. UNIQUE
Rationale: The UNIQUE constraint ensures that all values in a column are distinct, preventing
duplicate entries.
Question 12: What does DDL stand for in SQL?
A. Data Definition Language
B. Data Manipulation Language
C. Data Control Language
D. Data Query Language
CORRECT ANSWER: A. Data Definition Language
Rationale: DDL refers to the subset of SQL commands used to define and modify database
structures, such as CREATE, ALTER, and DROP.
Question 13: Which operator is used to search for a specified pattern in a column?
A. FROM
B. LIKE
C. IN
D. BETWEEN
CORRECT ANSWER: B. LIKE
Rationale: The LIKE operator is used in a WHERE clause to search for a specified pattern in a
column, often using wildcards.
Question 14: What is a view in a database?
A. A physical table storing data
B. A virtual table based on the result-set of an SQL statement
C. A backup of the database
D. A user permission level
CORRECT ANSWER: B. A virtual table based on the result-set of an SQL statement
Rationale: A view is a virtual table whose contents are defined by a query. It does not store
data itself but displays data from underlying tables.
Question 15: Which transaction isolation level prevents dirty reads?
A. Read Uncommitted
B. Read Committed
C. Repeatable Read
D. Serializable
CORRECT ANSWER: B. Read Committed
Rationale: Read Committed ensures that any data read is committed at the moment it is read,
thus preventing dirty reads.
, Question 16: What is the function of the GROUP BY clause?
A. To filter groups after aggregation
B. To sort the result set
C. To arrange identical data into groups
D. To join multiple tables
CORRECT ANSWER: C. To arrange identical data into groups
Rationale: The GROUP BY statement groups rows that have the same values into summary
rows, often used with aggregate functions.
Question 17: Which command is used to change the data type of a column?
A. UPDATE
B. MODIFY
C. ALTER TABLE
D. CHANGE COLUMN
CORRECT ANSWER: C. ALTER TABLE
Rationale: The ALTER TABLE command is used to add, delete, or modify columns in an existing
table, including changing data types.
Question 18: What is a stored procedure?
A. A backup script
B. A prepared SQL code that can be saved and reused
C. A type of index
D. A user role
CORRECT ANSWER: B. A prepared SQL code that can be saved and reused
Rationale: A stored procedure is a prepared SQL code that you can save, so the code can be
reused over and over again.
Question 19: Which normal form requires that there are no repeating groups?
A. 1NF
B. 2NF
C. 3NF
D. 4NF
CORRECT ANSWER: A. 1NF
Rationale: First Normal Form (1NF) requires that each column contains atomic values and there
are no repeating groups of columns.
Question 20: What is the purpose of the HAVING clause?
A. To filter records before grouping
B. To filter groups after aggregation
C. To sort the results
D. To join tables
CORRECT ANSWER: B. To filter groups after aggregation
Rationale: The HAVING clause was added to SQL because the WHERE keyword could not be
used with aggregate functions; it filters groups after the GROUP BY clause.
Question 21: Which SQL statement is used to update data in a database?
Study Guide – WGU C949 Practice Questions, Verified
Answers, Algorithm Concepts, Coding Logic, and Exam
Preparation Materials for Western Governors University
Students
Question 1: Which SQL command is used to retrieve data from a database?
A. INSERT
B. UPDATE
C. SELECT
D. DELETE
CORRECT ANSWER: C. SELECT
Rationale: The SELECT statement is the fundamental SQL command used to query and retrieve
data from one or more tables in a relational database.
Question 2: What does ACID stand for in the context of database transactions?
A. Atomicity, Consistency, Isolation, Durability
B. Accuracy, Consistency, Integrity, Durability
C. Atomicity, Clarity, Isolation, Dependency
D. Availability, Consistency, Isolation, Durability
CORRECT ANSWER: A. Atomicity, Consistency, Isolation, Durability
Rationale: ACID is a set of properties of database transactions intended to guarantee validity
even in the event of errors, power failures, etc. It stands for Atomicity, Consistency, Isolation,
and Durability.
Question 3: Which normal form eliminates transitive dependencies?
A. First Normal Form (1NF)
B. Second Normal Form (2NF)
C. Third Normal Form (3NF)
D. Boyce-Codd Normal Form (BCNF)
CORRECT ANSWER: C. Third Normal Form (3NF)
Rationale: Third Normal Form (3NF) requires that the table is in 2NF and all non-key attributes
are not transitively dependent on the primary key.
Question 4: What is the primary key in a relational database table?
A. A key that allows null values
B. A unique identifier for each record in a table
C. A key used to link two tables together
D. A key that can be duplicated across records
CORRECT ANSWER: B. A unique identifier for each record in a table
Rationale: A primary key is a specific choice of a minimal set of attributes (columns) that
uniquely specify a tuple (row) in a relation (table). It cannot contain null values.
Question 5: Which clause is used to filter records in a SQL query?
A. ORDER BY
B. GROUP BY
C. WHERE
D. HAVING
,CORRECT ANSWER: C. WHERE
Rationale: The WHERE clause is used to extract only those records that fulfill a specified
condition before any grouping occurs.
Question 6: What type of join returns all records when there is a match in either left or right
table?
A. INNER JOIN
B. LEFT JOIN
C. RIGHT JOIN
D. FULL OUTER JOIN
CORRECT ANSWER: D. FULL OUTER JOIN
Rationale: A FULL OUTER JOIN returns all records when there is a match in either the left or
right table records, filling in NULLs for missing matches.
Question 7: Which command is used to remove a table from a database?
A. DELETE TABLE
B. REMOVE TABLE
C. DROP TABLE
D. ERASE TABLE
CORRECT ANSWER: C. DROP TABLE
Rationale: The DROP TABLE command is used to delete the table structure and all data stored
within it from the database.
Question 8: What is a foreign key?
A. A key that uniquely identifies a record in another table
B. A key used to encrypt data
C. A key that allows duplicate values only
D. A key used to sort data alphabetically
CORRECT ANSWER: A. A key that uniquely identifies a record in another table
Rationale: A foreign key is a field (or collection of fields) in one table that refers to the primary
key in another table, establishing a link between the two.
Question 9: Which SQL function is used to count the number of rows?
A. SUM()
B. COUNT()
C. AVG()
D. TOTAL()
CORRECT ANSWER: B. COUNT()
Rationale: The COUNT() function returns the number of rows that matches a specified criterion.
Question 10: What is the purpose of an index in a database?
A. To secure data from unauthorized access
B. To speed up data retrieval operations
C. To store backup copies of data
D. To enforce data types
CORRECT ANSWER: B. To speed up data retrieval operations
,Rationale: An index is a data structure that improves the speed of data retrieval operations on a
database table at the cost of additional writes and storage space.
Question 11: Which constraint ensures that all values in a column are different?
A. NOT NULL
B. UNIQUE
C. DEFAULT
D. CHECK
CORRECT ANSWER: B. UNIQUE
Rationale: The UNIQUE constraint ensures that all values in a column are distinct, preventing
duplicate entries.
Question 12: What does DDL stand for in SQL?
A. Data Definition Language
B. Data Manipulation Language
C. Data Control Language
D. Data Query Language
CORRECT ANSWER: A. Data Definition Language
Rationale: DDL refers to the subset of SQL commands used to define and modify database
structures, such as CREATE, ALTER, and DROP.
Question 13: Which operator is used to search for a specified pattern in a column?
A. FROM
B. LIKE
C. IN
D. BETWEEN
CORRECT ANSWER: B. LIKE
Rationale: The LIKE operator is used in a WHERE clause to search for a specified pattern in a
column, often using wildcards.
Question 14: What is a view in a database?
A. A physical table storing data
B. A virtual table based on the result-set of an SQL statement
C. A backup of the database
D. A user permission level
CORRECT ANSWER: B. A virtual table based on the result-set of an SQL statement
Rationale: A view is a virtual table whose contents are defined by a query. It does not store
data itself but displays data from underlying tables.
Question 15: Which transaction isolation level prevents dirty reads?
A. Read Uncommitted
B. Read Committed
C. Repeatable Read
D. Serializable
CORRECT ANSWER: B. Read Committed
Rationale: Read Committed ensures that any data read is committed at the moment it is read,
thus preventing dirty reads.
, Question 16: What is the function of the GROUP BY clause?
A. To filter groups after aggregation
B. To sort the result set
C. To arrange identical data into groups
D. To join multiple tables
CORRECT ANSWER: C. To arrange identical data into groups
Rationale: The GROUP BY statement groups rows that have the same values into summary
rows, often used with aggregate functions.
Question 17: Which command is used to change the data type of a column?
A. UPDATE
B. MODIFY
C. ALTER TABLE
D. CHANGE COLUMN
CORRECT ANSWER: C. ALTER TABLE
Rationale: The ALTER TABLE command is used to add, delete, or modify columns in an existing
table, including changing data types.
Question 18: What is a stored procedure?
A. A backup script
B. A prepared SQL code that can be saved and reused
C. A type of index
D. A user role
CORRECT ANSWER: B. A prepared SQL code that can be saved and reused
Rationale: A stored procedure is a prepared SQL code that you can save, so the code can be
reused over and over again.
Question 19: Which normal form requires that there are no repeating groups?
A. 1NF
B. 2NF
C. 3NF
D. 4NF
CORRECT ANSWER: A. 1NF
Rationale: First Normal Form (1NF) requires that each column contains atomic values and there
are no repeating groups of columns.
Question 20: What is the purpose of the HAVING clause?
A. To filter records before grouping
B. To filter groups after aggregation
C. To sort the results
D. To join tables
CORRECT ANSWER: B. To filter groups after aggregation
Rationale: The HAVING clause was added to SQL because the WHERE keyword could not be
used with aggregate functions; it filters groups after the GROUP BY clause.
Question 21: Which SQL statement is used to update data in a database?
