Free Practice Questions for WGU Data Management - Foundations Exam

Answer : A

An aggregate function performs a calculation over multiple rows and returns a single value. Examples include SUM(), AVG(), MAX(), MIN(), and COUNT() in SQL.

Option A (Correct): Aggregate functions compute values over a set of rows, like summing total sales or averaging grades.

Option B (Incorrect): Selecting rows that appear in one table but not another is done using set operations (EXCEPT or MINUS in SQL).

Option C (Incorrect): Eliminating columns is done using the PROJECT operation or SELECT with specific columns.

Option D (Incorrect): Combining rows from two tables refers to a JOIN operation, not aggregation.

Answer : D

The WHERE clause is used in SQL SELECT statements to limit the number of rows that match a specific condition. It helps filter data based on given criteria before retrieving the results.

Example Usage:

sql

SELECT *

FROM Employees

WHERE Salary > 50000;

This query limits the result set to employees whose salary is greater than 50,000.

Why Other Options Are Incorrect:

Option A (FROM) (Incorrect): Specifies the table from which data is retrieved but does not limit results.

Option B (DROP) (Incorrect): Used for deleting tables, databases, or views, not filtering rows.

Option C (INTO) (Incorrect): Used in statements like INSERT INTO or SELECT INTO, which do not filter results.

Thus, WHERE is the correct keyword for applying a limiter in a SELECT statement.

Answer : A

Cardinality defines the minimum and maximum number of occurrences of one entity in relation to another.

Example Usage in an ER Model:

One-to-Many (1:M): A customer can place multiple orders, but each order belongs to only one customer.

Customers (1) --------- (M) Orders

Cardinality notation:

(1,1) One-to-One

(0,M) Zero-to-Many

(1,M) One-to-Many

Why Other Options Are Incorrect:

Option B (Physical design) (Incorrect): Focuses on storage and indexing, not relationships.

Option C (Attribute minimum) (Incorrect): No such formal term in database modeling.

Option D (Partition) (Incorrect): Refers to dividing tables, not relationship constraints.

Thus, the correct answer is Cardinality, as it defines min/max constraints on relationships.

Answer : D

An index scan is a database operation that quickly locates table blocks using an index rather than scanning the entire table. It significantly improves query performance.

Example Usage:

sql

SELECT * FROM Employees WHERE EmployeeID = 105;

If EmployeeID is indexed, the database uses an index scan to quickly find the record.

Why Other Options Are Incorrect:

Option A (Binary search) (Incorrect): A searching algorithm, but not a database operation.

Option B (Table scan) (Incorrect): Scans the entire table, which is slower than an index scan.

Option C (Fan-out) (Incorrect): Refers to branching in B-Trees but does not locate table blocks directly.

Thus, the correct answer is Index scan, as it efficiently locates table blocks.

Answer : B

The HAVING clause is used in SQL to filter grouped results generated by the GROUP BY clause. Unlike WHERE, which filters individual rows before grouping, HAVING filters after aggregation has been performed.

Example Usage:

sql

SELECT Department, AVG(Salary) AS AvgSalary

FROM Employees

GROUP BY Department

HAVING AVG(Salary) > 50000;

This query first groups employees by Department, calculates the average salary per department, and then filters only those departments where the average salary is greater than 50,000.

Why Other Options Are Incorrect:

Option A (REPLACE) (Incorrect): Used for string substitution, not filtering.

Option C (WITH) (Incorrect): Used in Common Table Expressions (CTEs), not for filtering.

Option D (WHERE) (Incorrect): Used for row-level filtering before aggregation, but it cannot be used on aggregate functions like SUM() or AVG().

Thus, HAVING is the correct answer for filtering after grouping.