Databricks Certified Data Engineer - Associate

Get started today

Ultimate access to all questions.

A data engineer is working with two tables. Each of these tables is displayed below in its entirety.

sales

customer_id	spend	units
a1	28.94	7
a3	874.12	23
a4	8.99	1

favorite_stores

customer_id	store_id
a1	s1
a2	s1
a4	s2

The data engineer runs the following query to join these tables together:

SELECT
    sales.customer_id,
    sales.spend,
    favorite_stores.store_id
FROM sales
LEFT JOIN favorite_stores
ON sales.customer_id = favorite_stores.customer_id;

SELECT
    sales.customer_id,
    sales.spend,
    favorite_stores.store_id
FROM sales
LEFT JOIN favorite_stores
ON sales.customer_id = favorite_stores.customer_id;

Which of the following will be returned by the above query?

Real Exam

Community

KKeng

Last updated: January 13, 2026 at 09:03

customer_id	spend	store_id
a1	28.94	s1
a4	8.99	s2

customer_id	spend	units	store_id
a1	28.94	7	s1
a4	8.99	1	s2

customer_id	spend	store_id
a1	28.94	s1
a3	874.12	NULL
a4	8.99	s2

customer_id	spend	store_id
a1	28.94	s1
a2	NULL	s1
a3	874.12	NULL
a4	8.99	s2

customer_id	spend	store_id
a1	28.94	s1
a2	NULL	s1
a4	8.99	s2

Explanation:

Explanation

The correct answer is C because:

LEFT JOIN returns all rows from the left table (sales) and matching rows from the right table (favorite_stores).
When there's no match in the right table, NULL values are returned for the right table's columns.
The SELECT statement only includes sales.customer_id, sales.spend, and favorite_stores.store_id - not the units column.

Analysis of each row:

a1: Exists in both tables → store_id = s1
a3: Exists only in sales table → store_id = NULL (no match in favorite_stores)
a4: Exists in both tables → store_id = s2

Why other options are incorrect:

A: Missing row for a3 (should be included in LEFT JOIN)
B: Includes units column (not in SELECT statement) and missing row for a3
D: Includes a2 (from favorite_stores only - not in sales table, so shouldn't appear in LEFT JOIN)
E: Includes a2 (from favorite_stores only) and missing row for a3

Key SQL JOIN concept:

LEFT JOIN preserves all rows from the left table regardless of whether they have matches in the right table.
Only columns specified in the SELECT clause appear in the result set.
The units column is not selected, so it doesn't appear in the output.

Powered ByGPT-5.2

Comments

Loading comments...