1. B
“SELECT * FROM table_name” retrieves all data and columns from the specified table.

2. D
“TRUNCATE” removes all rows in the table without removing the table itself.

3. B
The “GROUP BY” clause groups rows that have the same values in specified columns into summary rows.

4. A
The DISTINCT keyword removes duplicate rows from the result set.

5. C
The “SUM()” function calculates the total sum of a numeric column.

6. A
The “JOIN” operation combines data from multiple tables based on a related column.

7. C
The “HAVING” clause is used to filter data after the “GROUP BY” operation.

8. B
“INNER JOIN” returns only matching rows from both tables.

9. A
The “ORDER BY” clause is used to sort data in ascending or descending order.

10. B
The “AVG()” function calculates the average of a numeric column.

11. B
The query counts the number of employees in department 50.

12. C
“FETCH FIRST 5 ROWS ONLY” retrieves the first 5 rows of the result set.

13. B
The “WHERE” clause is used to specify conditions for filtering results.

14. A
“CREATE TABLE” defines a new table with columns and datatypes.

15. A
The default sorting order is ascending when using “ORDER BY”.

16. A
The “UNION” clause combines two result sets into one.

17. C
The “MAX()” function returns the highest value in a column.

18. B
“ALTER TABLE” modifies the structure of an existing table.

19. C
“ALTER TABLE” allows you to modify an existing column in a table.

20. A
The query returns employees whose salary is greater than 50000.

21. A
The “BETWEEN” keyword returns records where values fall within a specified range.

22. A
“GROUP BY HAVING COUNT(*) ＞ 1” is used to find duplicate records.

23. B
“VARCHAR” is used to store variable-length strings.

24. B
“TRUNCATE TABLE” removes all records from the table without deleting the table.

25. A
The “LIKE” operator is used for pattern matching in SQL queries.

26. A
The “DISTINCT” keyword removes duplicates from the result set.

27. B
“JOIN” is used to combine data from multiple tables.

28. A
“CONCAT（）” concatenates two or more strings together.

29. C
Oracle SQL will return an error if you try to insert a duplicate primary key.

30. C
The “CONSTRAINT” keyword is used to define primary key constraints in SQL.

31. B
The “UPPER()” function converts a string to uppercase.

32. A
“ALTER TABLE … ADD” is used to add a new column to an existing table.

33. A
“WHERE salary IS NULL” retrieves records where the salary field is not assigned a value.

34. C
“ALTER TABLE” is used to modify the structure of a table, including changing the datatype of a column.

35. C
The “IS NULL” condition is used to check for missing or undefined values (NULL) in a column.