WGU D426 – DATA MANAGEMENT FOUNDATIONS v3 COMPREHENSIVE |VERIFIED ANSWERS AND QUESTIONS - MOST RECENT EDITION 2026/2027

WGU D426 – DATA MANAGEMENT FOUNDATIONS v3 COMPREHENSIVE
|VERIFIED ANSWERS AND QUESTIONS - MOST RECENT EDITION 2026/2027




# QUESTION ANSWER
What does SQL stand for? Structured Query Language — a
1 standard language for managing and
querying relational databases.
What is the basic syntax of a SELECT column(s) FROM
SELECT statement? table_name WHERE condition; —
2
retrieves specified columns from a
table matching the condition.
How do you select all columns SELECT * FROM Employees; — the
3 from a table called Employees? asterisk (*) is a wildcard that selects
every column.
What clause filters rows in a The WHERE clause filters rows based
4 SELECT statement? on a condition, e.g., WHERE Salary >
50000.
What is the difference between WHERE filters individual rows before
5 WHERE and HAVING? grouping; HAVING filters groups
after GROUP BY has been applied.
What does ORDER BY do? ORDER BY sorts the result set by one
or more columns, either ASC
6
(ascending, default) or DESC
(descending).
How do you eliminate duplicate Use SELECT DISTINCT
rows in a query result? column_name FROM table; —
7
DISTINCT removes duplicate values
from the result.



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, What does LIMIT (or TOP in Restricts the number of rows returned.
SQL Server) do? E.g., SELECT * FROM Orders
8
LIMIT 10; returns only the first 10
rows.
What is an alias in SQL? An alias renames a column or table
temporarily using AS. E.g., SELECT
9
FirstName AS Name FROM
Employees;
How do you concatenate strings Use CONCAT(str1, str2) in
in SQL? MySQL/standard SQL, or the ||
10
operator in Oracle/PostgreSQL. E.g.,
CONCAT(FirstName, ' ', LastName).
What does the LIKE operator LIKE is used in WHERE clauses for
do? pattern matching. % matches any
11
sequence of characters; _ matches
exactly one character.
What is the wildcard % used % represents zero or more characters
for in SQL? in a LIKE pattern. E.g., WHERE
12
Name LIKE 'J%' finds names starting
with J.
What does WHERE Name It returns names where any single
13 LIKE '_ohn' return? character precedes 'ohn', such as 'John'
or 'Bohn'.
What is the IN operator in IN checks if a value matches any
14 SQL? value in a list. E.g., WHERE
Department IN ('HR', 'IT', 'Finance').
What does BETWEEN do in BETWEEN tests whether a value is
SQL? within a range (inclusive). E.g.,
15
WHERE Salary BETWEEN 40000
AND 80000.
How do you test for NULL Use IS NULL or IS NOT NULL. E.g.,
16 values in SQL? WHERE ManagerID IS NULL. You
cannot use = NULL.




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, What is the difference between NULL means unknown/missing data.
17 NULL and 0 or empty string? 0 is a numeric value; an empty string ''
is a zero-length string. NULL ≠ 0 ≠ ''.
What does COALESCE do? COALESCE returns the first non-
NULL value in a list. E.g.,
18
COALESCE(Phone, Email, 'N/A')
returns the first non-null contact.
What is a subquery? A subquery is a SELECT statement
19 nested inside another SQL statement,
used to return data for the outer query.
What is a correlated subquery? A correlated subquery references
columns from the outer query and is
20
re-evaluated for each row of the outer
query.
What does EXISTS do in SQL? EXISTS returns TRUE if the subquery
returns at least one row. E.g., WHERE
21
EXISTS (SELECT 1 FROM Orders
WHERE CustomerID = c.ID).
What is the difference between UNION combines result sets and
UNION and UNION ALL? removes duplicates; UNION ALL
22
combines them and keeps all
duplicates (faster).
What is required for UNION to Both SELECT statements must have
23 work? the same number of columns with
compatible data types.
What does INTERSECT INTERSECT returns only the rows
24
return? that appear in both result sets.
What does EXCEPT (or EXCEPT returns rows from the first
25 MINUS) return? result set that do not appear in the
second result set.
What is a CASE expression in CASE is SQL's conditional
SQL? expression. E.g., CASE WHEN Salary
26
> 70000 THEN 'High' ELSE 'Low'
END AS SalaryBand.


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, What does NULLIF do? NULLIF(expr1, expr2) returns NULL
if both expressions are equal;
27
otherwise returns expr1. Used to avoid
divide-by-zero.
What is the purpose of the FROM specifies the table(s) from
28 FROM clause? which to retrieve data. Multiple tables
trigger a join.
Can SELECT be used without a Yes, in some databases. E.g., SELECT
29 FROM clause? 1+1; or SELECT GETDATE(); to
evaluate expressions without a table.
What does SELECT TOP 5 * Returns the 5 rows with the highest
30 FROM Sales ORDER BY Amount from the Sales table.
Amount DESC do?
What is a derived table? A derived table is a subquery used in
31 the FROM clause, treated as a
temporary table. It must be aliased.
How do you comment in SQL? Single-line: -- comment text. Multi-
32
line: /* comment block */.
What is the FETCH/OFFSET Used for pagination. E.g., OFFSET 10
clause used for? ROWS FETCH NEXT 5 ROWS
33
ONLY skips the first 10 rows and
returns the next 5.
What does SELECT It returns each unique city value once,
34 DISTINCT City FROM removing duplicate city names from
Customers return? the Customers table.
What is the difference between = checks for exact equality; LIKE
35 = and LIKE? allows pattern matching with
wildcards (% and _).
What data types are commonly INT, BIGINT, VARCHAR(n),
used in SQL? CHAR(n), DATE, DATETIME,
36
DECIMAL(p,s), FLOAT,
BOOLEAN, TEXT.
What is VARCHAR vs CHAR? CHAR(n) is fixed-length;
37
VARCHAR(n) is variable-length up to

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