Explanation:
The correct answer is C because:
sales) and matching rows from the right table (favorite_stores).NULL values are returned for the right table's columns.sales.customer_id, sales.spend, and favorite_stores.store_id.Analysis of each row:
store_id = s1sales table → store_id = NULL (no match in favorite_stores)store_id = s2favorite_stores → NOT included because LEFT JOIN starts from sales tableWhy other options are incorrect:
a3 (should be included with NULL store_id)units column (not selected in query) and missing row for a3a2 (should not be included as it's not in sales table)a2 (should not be included) and missing row for a3Ultimate access to all questions.
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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?
A
| customer_id | spend | store_id |
|---|---|---|
| a1 | 28.94 | s1 |
| a4 | 8.99 | s2 |
B
| customer_id | spend | units | store_id |
|---|---|---|---|
| a1 | 28.94 | 7 | s1 |
| a4 | 8.99 | 1 | s2 |
C
| customer_id | spend | store_id |
|---|---|---|
| a1 | 28.94 | s1 |
| a3 | 874.12 | NULL |
| a4 | 8.99 | s2 |
D
| customer_id | spend | store_id |
|---|---|---|
| a1 | 28.94 | s1 |
| a2 | NULL | s1 |
| a3 | 874.12 | NULL |
| a4 | 8.99 | s2 |
E
| customer_id | spend | store_id |
|---|---|---|
| a1 | 28.94 | s1 |
| a2 | NULL | s1 |
| a4 | 8.99 | s2 |