DML (INSERT, UPDATE, DELETE) in DBMS Theory - Interactive Code Practice

Practice - 5 Tasks

1fill in blank

easy

Complete the code to insert a new record into the table.

DBMS Theory

INSERT INTO employees (name, age) VALUES ([1], 30);

Drag options to blanks, or click blank then click option'

A'John'

Bname

C"John"

DJohn

Attempts:

3 left

💡 Hint

Common Mistakes

Forgetting to use quotes around text values.

Using double quotes instead of single quotes.

The value for a text field must be enclosed in single quotes in SQL. So, 'John' is correct.

2fill in blank

medium

Complete the code to update the age of an employee named 'Alice'.

DBMS Theory

UPDATE employees SET age = 35 WHERE name = [1];

Drag options to blanks, or click blank then click option'

A"Alice"

B'Alice'

CAlice

Dname

Attempts:

3 left

💡 Hint

Common Mistakes

Using the column name instead of the string value.

Using double quotes instead of single quotes.

In SQL, string literals must be enclosed in single quotes. So, 'Alice' is correct.

3fill in blank

hard

Fix the error in the DELETE statement to remove employees older than 60.

DBMS Theory

DELETE FROM employees WHERE age [1] 60;

Drag options to blanks, or click blank then click option'

A<

B=

C!=

D>

Attempts:

3 left

💡 Hint

Common Mistakes

Using '=' which deletes only employees exactly 60 years old.

Using '<' which deletes employees younger than 60.

To delete employees older than 60, the condition must be age > 60.

4fill in blank

hard

Fill both blanks to update the salary of employees in the 'Sales' department to 50000.

DBMS Theory

UPDATE employees SET salary = [1] WHERE department [2] 'Sales';

Drag options to blanks, or click blank then click option'

A50000

BMarketing

C=

D>

Attempts:

3 left

💡 Hint

Common Mistakes

Using '>' instead of '=' in the WHERE clause.

Putting quotes around the number 50000.

The salary should be set to 50000, and the department must equal 'Sales' to update only those employees.

5fill in blank

hard

Fill all three blanks to insert a new employee with name 'Emma', age 28, and department 'HR'.

DBMS Theory

INSERT INTO employees (name, age, department) VALUES ([1], [2], [3]);

Drag options to blanks, or click blank then click option'

A'Emma'

B28

C'HR'

DEmma

Attempts:

3 left

💡 Hint

Common Mistakes

Forgetting quotes around text values.

Putting quotes around numbers.

Text values like name and department need single quotes. Age is a number and does not need quotes.

Practice

1. Which DML command is used to add new rows to a database table?

easy

A. INSERT

B. UPDATE

C. DELETE

D. SELECT

Solution

1. Step 1: Understand the purpose of DML commands

   DML commands are used to manipulate data in tables: adding, changing, or removing rows.

2. Step 2: Identify the command for adding rows

   The INSERT command adds new rows, UPDATE changes existing rows, and DELETE removes rows.

3. Final Answer:

   INSERT -> Option A

4. Quick Check:

   Add new rows = INSERT [OK]

Hint: Add new data? Use INSERT command [OK]

Common Mistakes:

• Confusing UPDATE with INSERT
• Using DELETE to add data
• Thinking SELECT adds data

2. Which of the following is the correct syntax to update the salary to 5000 for employee with id 10?

easy

A. UPDATE employees SET salary 5000 WHERE id = 10;

B. UPDATE employees salary = 5000 WHERE id = 10;

C. UPDATE employees SET salary = 5000 WHERE id = 10;

D. UPDATE employees SET salary = 5000;

Solution

1. Step 1: Recall the UPDATE syntax

   The correct syntax is UPDATE table_name SET column = value WHERE condition; to update specific rows.

2. Step 2: Check each option

   UPDATE employees SET salary = 5000 WHERE id = 10; matches the correct syntax with a WHERE clause to target employee id 10. Options B and C miss the SET keyword or equal sign. UPDATE employees SET salary = 5000; lacks WHERE, so it updates all rows.

3. Final Answer:

   UPDATE employees SET salary = 5000 WHERE id = 10; -> Option C

4. Quick Check:

   UPDATE with SET and WHERE = UPDATE employees SET salary = 5000 WHERE id = 10; [OK]

Hint: UPDATE needs SET and WHERE for specific rows [OK]

Common Mistakes:

• Omitting SET keyword
• Missing WHERE clause
• Wrong assignment syntax

3. Consider the table products with columns id, name, and price. What will be the result of this query?

DELETE FROM products WHERE price < 100;

medium

A. All products with price greater than 100 will be removed.

B. All products with price less than 100 will be removed.

C. No products will be removed because condition is incorrect.

D. Syntax error due to missing semicolon.

Solution

1. Step 1: Understand DELETE with WHERE condition

   The DELETE command removes rows matching the WHERE condition. Here, it targets rows where price is less than 100.

2. Step 2: Analyze the condition and syntax

   The condition price < 100 correctly selects products priced below 100. The semicolon is optional in many systems but good practice.

3. Final Answer:

   All products with price less than 100 will be removed. -> Option B

4. Quick Check:

   DELETE with price < 100 removes matching rows [OK]

Hint: DELETE removes rows matching WHERE condition [OK]

Common Mistakes:

• Confusing less than with greater than
• Thinking DELETE needs all rows
• Assuming syntax error without semicolon

4. Identify the error in this SQL statement:

UPDATE employees SET salary = 6000 WHERE;

medium

A. Missing condition after WHERE clause.

B. Incorrect use of SET keyword.

C. Salary value should be in quotes.

D. UPDATE cannot be used without DELETE.

Solution

1. Step 1: Check the UPDATE statement structure

   UPDATE requires SET to assign new values and WHERE to specify which rows to update.

2. Step 2: Identify the error in the WHERE clause

   The statement ends with WHERE but no condition follows, which is a syntax error.

3. Final Answer:

   Missing condition after WHERE clause. -> Option A

4. Quick Check:

   WHERE must have a condition [OK]

Hint: WHERE must always have a condition [OK]

Common Mistakes:

• Leaving WHERE empty
• Putting value in quotes unnecessarily
• Confusing UPDATE with DELETE

5. You want to increase the price by 10% for all products priced below 50. Which SQL statement correctly does this?

hard

A. UPDATE products SET price = price + 0.10 WHERE price < 50;

B. UPDATE products SET price = price + 10 WHERE price < 50;

C. UPDATE products SET price = price * 0.10 WHERE price < 50;

D. UPDATE products SET price = price * 1.10 WHERE price < 50;

Solution

1. Step 1: Understand the requirement to increase price by 10%

   Increasing by 10% means multiplying the current price by 1.10 (100% + 10%).

2. Step 2: Analyze each option

   UPDATE products SET price = price * 1.10 WHERE price < 50; correctly multiplies price by 1.10 for prices less than 50. UPDATE products SET price = price + 10 WHERE price < 50; adds 10 units, not 10%. UPDATE products SET price = price * 0.10 WHERE price < 50; multiplies by 0.10, reducing price. UPDATE products SET price = price + 0.10 WHERE price < 50; adds 0.10 units, a small increase.

3. Final Answer:

   UPDATE products SET price = price * 1.10 WHERE price < 50; -> Option D

4. Quick Check:

   Multiply price by 1.10 to increase by 10% [OK]

Hint: Multiply by 1.10 to increase by 10% [OK]

Common Mistakes:

• Adding fixed amount instead of percentage
• Multiplying by 0.10 reduces price
• Forgetting WHERE clause