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A data engineer wants to horizontally combine two tables as a part of a query. They want to use a shared column as a key column, and they only want the query result to contain rows whose value in the key column is present in both tables.
Which of the following SQL commands can they use to accomplish this task?
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KKeng
A
INNER JOIN
B
OUTER JOIN
C
LEFT JOIN
D
MERGE
E
UNION
Explanation:
Explanation
An INNER JOIN is the correct SQL command for this scenario because:
- Horizontal combination: INNER JOIN combines tables horizontally (side-by-side) based on a common key column
- Shared column as key: INNER JOIN uses a shared column (or columns) to match rows between tables
- Rows present in both tables: INNER JOIN returns only rows where the key value exists in BOTH tables
Why other options are incorrect:
- B. OUTER JOIN: This typically refers to FULL OUTER JOIN, which returns all rows from both tables, including rows that don't have matches in the other table
- C. LEFT JOIN: Returns all rows from the left table and matching rows from the right table, including rows from the left table that don't have matches in the right table
- D. MERGE: This is not a standard SQL JOIN type; it's typically used for upsert operations (UPDATE/INSERT) in some database systems
- E. UNION: Combines tables vertically (stacking rows), not horizontally, and requires the same column structure
Example:
SELECT *
FROM table1
INNER JOIN table2
ON table1.key_column = table2.key_column;
SELECT *
FROM table1
INNER JOIN table2
ON table1.key_column = table2.key_column;
This query will return only rows where the key_column value exists in both table1 and table2.
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