DBMS-1

Which of the following is not allowed when a table already has data in it?

• ALTER TABLE ADD COLUMN

• ALTER TABLE DROP COLUMN

• ALTER TABLE RENAME COLUMN

• ALTER TABLE MODIFY COLUMN data type

What does the following SQL command do?
TRUNCATE TABLE employees;

• Deletes all rows and can't be rolled back

• Deletes all rows and can be rolled back

• Deletes the table structure and data

• Deletes rows based on WHERE clause

What will be the result of this query?
SELECT * FROM students WHERE marks = NULL;

• All rows with marks = NULL

• Syntax error

• No rows selected

• Only NULL rows returned

Which DML command can insert multiple rows in one statement?

• INSERT INTO ... VALUES

• INSERT ALL

• INSERT EACH

• APPEND ROWS

Which query will give you the 3rd highest salary from a salaries table?

• SELECT salary FROM salaries ORDER BY salary DESC LIMIT 3;

• SELECT MAX(salary) FROM salaries LIMIT 2,1;

• SELECT salary FROM (SELECT DISTINCT salary FROM salaries ORDER BY salary DESC LIMIT 2,1);

• SELECT salary FROM salaries OFFSET 2 ROWS FETCH NEXT 1 ROW ONLY;

Which of the following commands creates a new copy of a table with only structure and no data?

• CREATE TABLE new_table LIKE old_table;

• CREATE TABLE new_table AS SELECT * FROM old_table;

• SELECT * INTO new_table FROM old_table;

• CREATE TABLE new_table FROM old_table;

What is the effect of this command: DELETE FROM orders WHERE 1=1;

• Deletes no rows

• Deletes all rows

• Deletes only rows with ID=1

• Causes syntax error

Which SQL clause is used only with DQL and not DML/DDL?

• WHERE

• ORDER BY

• HAVING

• GROUP BY

What is the output of the query:
SELECT DISTINCT city FROM customers ORDER BY city DESC;

• Duplicates included, sorted descending

• Unique cities in descending order

• Syntax error

• Duplicates in random order

What does SELECT DISTINCT dept, COUNT(*) FROM emp GROUP BY dept; return?

• Unique departments only

• Duplicates removed after grouping

• Syntax error

• Same result as SELECT dept, COUNT(*) ...