Question

Which of the following is true about the SQL JOIN operation?

• A. It combines rows from two or more tables based on a related column
• B. It only works on columns with unique values
• C. It is used for updating data in a table
• D. It can only be used to select data from one table at a time

Hint:

To understand SQL JOIN:
- Use JOIN to combine tables based on related columns (e.g., ID fields).
- Learn types: INNER JOIN, LEFT JOIN, RIGHT JOIN, FULL JOIN.
- Practice with simple queries to see row combinations.

Answer 1

The Correct Option is A

To determine the correct statement about the SQL JOIN operation, we need to understand its purpose and functionality in database management.
Step 1: Understand the SQL JOIN Operation
The JOIN operation in SQL is used to combine rows from two or more tables based on a related column, typically a foreign key or a common field.
It allows retrieval of data from multiple tables in a single query, based on a condition.
Step 2: Analyze Option A - It combines rows from two or more tables based on a related column
This accurately describes the primary function of a JOIN operation, such as INNER JOIN, LEFT JOIN, RIGHT JOIN, or FULL JOIN, which link tables using a related column (e.g., a primary key in one table and a foreign key in another).
Thus, option A is correct.
Step 3: Analyze Option B - It only works on columns with unique values
A JOIN operation does not require columns to have unique values; it works with related columns regardless of uniqueness (e.g., non-unique foreign keys are common).
Uniqueness is relevant for primary keys, but not a requirement for JOINs.
Thus, option B is incorrect.
Step 4: Analyze Option C - It is used for updating data in a table
The UPDATE statement, not JOIN, is used to modify data in a table.
JOIN is used for querying and combining data, not for updates (though it can be part of an UPDATE query with a JOIN clause).
Thus, option C is incorrect.
Step 5: Analyze Option D - It can only be used to select data from one table at a time
JOIN is specifically designed to select data from multiple tables by combining rows based on related columns.
Limiting it to one table contradicts its purpose.
Thus, option D is incorrect.
Step 6: Conclusion
The core function of a SQL JOIN is to combine data from multiple tables, making option A the correct choice.