Databricks Certified Data Engineer - Associate

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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 query selects only sales.customer_id, sales.spend, and favorite_stores.store_id.

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
a2: Exists only in favorite_stores → NOT included because LEFT JOIN starts from sales table

Why other options are incorrect:

A: Missing row for a3 (should be included with NULL store_id)
B: Includes units column (not selected in query) and missing row for a3
D: Includes row for a2 (should not be included as it's not in sales table)
E: Includes row for a2 (should not be included) and missing row for a3

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