Which SQL statement is used to add a new column to existing table?

The correct answer is B: ALTER TABLE ... ADD. ALTER TABLE ... ADD COLUMN syntax is correct for adding columns. Other options are invalid SQL syntax.

In a manufacturing database, to find products with sales in ALL regions, which approach is correct?

The correct answer is A: SELECT product_id FROM sales GROUP BY product_id HAVING COUNT(DISTINCT region) = (SELECT COUNT(*) FROM regions). Counts distinct regions per product and compares to total regions. Option B doesn't ensure ALL regions. Option C only checks one region. Option D is incomplete.

Which of the following is the correct order of SQL clause execution?

The correct answer is A: SELECT → WHERE → GROUP BY → HAVING → ORDER BY. SQL execution order: FROM → WHERE → GROUP BY → HAVING → SELECT → ORDER BY. WHERE is applied before grouping, HAVING after.

What is the difference between UNION and UNION ALL in SQL?

The correct answer is B: UNION removes duplicates; UNION ALL includes duplicates. UNION removes duplicate rows from the result, while UNION ALL includes all rows with duplicates.

What is the purpose of the JOIN clause in SQL?

The correct answer is A: To combine rows from two or more tables based on related columns. JOIN combines rows from two or more tables based on a relationship between the columns (usually foreign key relationship).