Quick Answer
The answer is NULL. This is correct because a LEFT JOIN retains every row from the left table, and for any row in the left table that has no matching row in the right table, SQL fills all columns from the right table with NULL, as defined by the ISO/IEC 9075 standard. On the CompTIA ITF+ FC0-U61 exam, this concept tests your understanding of outer join behavior, often appearing in scenario-based questions where you must predict output for customers without orders. A common trap is assuming those columns show zero or an empty string, but SQL uses NULL to represent the absence of a value. To remember this, think of the LEFT JOIN as a “keep everything, fill the gaps” operation: the left side is always present, and missing right-side data becomes NULL.
This FC0-U61 practice question tests your understanding of database fundamentals. Examine the command output carefully: the correct answer depends on what the output actually shows, not on general recall alone. After answering, compare your reasoning against the explanation and wrong-answer breakdown below. Once you have made your selection, read the full explanation to reinforce the concept and understand why each distractor is designed to mislead on exam day.
A query uses a LEFT JOIN between Customers and Orders. The result set includes customers with no orders. What does the Orders columns show for those customers?
NULL
LEFT JOIN produces NULL when no match.
The same as the customer ID
Why wrong: No, it's NULL.
Zero
Why wrong: NULL is used to indicate missing data, not zero.
Empty string
Why wrong: NULL is used, not empty string.
Answer choices
Answer the question above first, then reveal the full breakdown to understand why each option is right or wrong.
Correct answer & explanation
NULL
In a LEFT JOIN, all rows from the left table (Customers) are retained, and for rows with no matching rows in the right table (Orders), the columns from the right table are filled with NULL. This is the standard SQL behavior defined by the SQL standard (ISO/IEC 9075). Therefore, for customers with no orders, the Orders columns show NULL, not zero, an empty string, or any other default value.
Key principle: Answer the scenario, not the keyword: identify the specific constraint before choosing the most familiar-sounding option.
Answer analysis
For each option: why learners choose it and why it is or isn't the right answer here.
NULL
Why this is correct
LEFT JOIN produces NULL when no match.
Related concept
Read the scenario before looking for a memorised answer.
The same as the customer ID
Why it's wrong here
No, it's NULL.
Zero
Why it's wrong here
NULL is used to indicate missing data, not zero.
Empty string
Why it's wrong here
NULL is used, not empty string.
Common exam traps
The trap here is that candidates often confuse NULL with zero or an empty string, thinking a missing record should show a default value like 0 or '', but SQL strictly uses NULL to represent the absence of a matching row in a LEFT JOIN.
Detailed technical explanation
Under the hood, a LEFT JOIN produces a Cartesian product of matching rows, and for non-matching left rows, the right-side columns are set to NULL, which is a special marker meaning 'unknown' or 'no data', not a value. This distinction is critical in SQL because NULL comparisons require IS NULL, not = NULL, and aggregate functions like COUNT(*) include NULL rows while COUNT(column) does not. In real-world scenarios, such as generating a report of all customers and their order totals, customers with no orders will show NULL in the total column, which must be handled with COALESCE to display 0 if desired.
Key takeaway
Answer the scenario, not the keyword: identify the specific constraint before choosing the most familiar-sounding option.
Real-world example
A practitioner preparing for the FC0-U61 exam encounters this exact type of scenario on the job. The correct answer here is not the most general option — it is the best answer for the specific constraint described. Answer the scenario, not the keyword: identify the specific constraint before choosing the most familiar-sounding option. Real exam questions reward reading the full scenario before eliminating options, because the constraint defines which answer fits.
What to study next
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FAQ
Database Fundamentals — This question tests Database Fundamentals — Read the scenario before looking for a memorised answer..
The correct answer is: NULL — In a LEFT JOIN, all rows from the left table (Customers) are retained, and for rows with no matching rows in the right table (Orders), the columns from the right table are filled with NULL. This is the standard SQL behavior defined by the SQL standard (ISO/IEC 9075). Therefore, for customers with no orders, the Orders columns show NULL, not zero, an empty string, or any other default value.
Identify which exam domain this question belongs to, review the core concept, then practise similar questions from the same domain.
Read the scenario before looking for a memorised answer.
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Last reviewed: Jun 25, 2026
This FC0-U61 practice question is part of Courseiva's free CompTIA certification practice question bank. Courseiva provides original exam-style practice questions with explanations, topic-based practice, mock exams, readiness tracking, and study analytics to help learners prepare for the FC0-U61 exam.
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