Soft delete pattern concept in SQL - Interactive Code Practice

Practice - 5 Tasks

1fill in blank

easy

Complete the code to select all active users who are not soft deleted.

SQL

SELECT * FROM users WHERE [1] = 0;

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

Ais_deleted

Bstatus

Cactive

Ddeleted

Attempts:

3 left

💡 Hint

Common Mistakes

Using the wrong column name like 'deleted' or 'status' which may not exist.

Filtering with 'active' which might not be a column.

The column is_deleted is commonly used to mark soft deleted rows. Rows with is_deleted = 0 are active.

2fill in blank

medium

Complete the code to soft delete a user by setting the soft delete flag.

SQL

UPDATE users SET [1] = 1 WHERE user_id = 42;

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

Adeleted

Bactive

Cstatus

Dis_deleted

Attempts:

3 left

💡 Hint

Common Mistakes

Trying to delete the row with DELETE statement instead of updating the flag.

Using a wrong column name.

To soft delete, set is_deleted to 1 for the target user.

3fill in blank

hard

Fix the error in the query to select only non-deleted products.

SQL

SELECT * FROM products WHERE [1] = 0;

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

Aactive

Bdeleted

Cis_deleted

Dstatus

Attempts:

3 left

💡 Hint

Common Mistakes

Using a column that does not exist like 'deleted' or 'status'.

Confusing the flag value (true/false vs 1/0).

The correct column to check is is_deleted. Using is_deleted = 0 filters active rows.

4fill in blank

hard

Fill both blanks to select all active orders and sort them by creation date descending.

SQL

SELECT * FROM orders WHERE [1] = 0 ORDER BY [2] DESC;

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

Ais_deleted

Bdeleted

Ccreated_at

Dorder_date

Attempts:

3 left

💡 Hint

Common Mistakes

Using the wrong column for filtering or sorting.

Sorting ascending instead of descending.

Use is_deleted = 0 to filter active orders and created_at to sort by creation date.

5fill in blank

hard

Fill all three blanks to insert a new user with soft delete flag set to active (not deleted).

SQL

INSERT INTO users (username, email, [1]) VALUES ([2], [3], 0);

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

Ais_deleted

B'newuser'

C'[e-mail]'

Ddeleted

Attempts:

3 left

💡 Hint

Common Mistakes

Using the wrong column name for the flag.

Not quoting string values in the VALUES clause.

Insert the is_deleted column with value 0 to mark the user as active. Provide username and email as strings.

Practice

1. What is the main idea behind the soft delete pattern in databases?

easy

A. Marking data as deleted without actually removing it from the table

B. Permanently removing data from the database

C. Backing up data before deletion

D. Encrypting data before deletion

Solution

1. Step 1: Understand soft delete concept

   Soft delete means we do not remove data but mark it as deleted.

2. Step 2: Compare options

   Only Marking data as deleted without actually removing it from the table describes marking data instead of removing it.

3. Final Answer:

   Marking data as deleted without actually removing it from the table -> Option A

4. Quick Check:

   Soft delete = Mark data deleted, not remove [OK]

Hint: Soft delete means mark deleted, don't remove [OK]

Common Mistakes:

• Thinking soft delete removes data physically
• Confusing soft delete with backup
• Assuming encryption is part of soft delete

2. Which of the following SQL table columns is commonly used to implement a soft delete?

easy

A. deleted_at TIMESTAMP

B. is_deleted BOOLEAN

C. delete_flag VARCHAR(10)

D. remove_date DATE

Solution

1. Step 1: Identify common soft delete column

   The most common column is a boolean named is_deleted to mark true/false.

2. Step 2: Check other options

   Other columns can be used but is_deleted BOOLEAN is standard and simplest.

3. Final Answer:

   is_deleted BOOLEAN -> Option B

4. Quick Check:

   Soft delete uses boolean flag = is_deleted [OK]

Hint: Soft delete uses boolean flag like is_deleted [OK]

Common Mistakes:

• Using timestamp instead of boolean for soft delete
• Choosing vague column names
• Confusing soft delete with audit columns

3. Given the table users with a boolean column is_deleted, what will this query return?

SELECT * FROM users WHERE is_deleted = FALSE;

medium

A. Only users not marked as deleted

B. Only users marked as deleted

C. No users, syntax error

D. All users including deleted ones

Solution

1. Step 1: Understand the WHERE clause

   The query filters rows where is_deleted is FALSE, meaning not deleted.

2. Step 2: Determine returned rows

   Only users not marked deleted will be returned, excluding soft deleted rows.

3. Final Answer:

   Only users not marked as deleted -> Option A

4. Quick Check:

   WHERE is_deleted = FALSE returns active users [OK]

Hint: WHERE is_deleted = FALSE filters active rows [OK]

Common Mistakes:

• Thinking it returns deleted users
• Assuming syntax error due to boolean
• Confusing TRUE and FALSE values

4. You have this query to select active users:

SELECT * FROM users WHERE is_deleted = 0;

But it returns no rows even though some users are active. What is the likely problem?

medium

A. The table has no data

B. The is_deleted column is missing

C. The query syntax is invalid

D. The column is_deleted uses TRUE/FALSE, not 0/1

Solution

1. Step 1: Check data type of is_deleted

   If is_deleted is BOOLEAN, it expects TRUE/FALSE, not numeric 0/1.

2. Step 2: Understand why query returns no rows

   Using 0 may not match FALSE in some SQL dialects, causing no rows returned.

3. Final Answer:

   The column is_deleted uses TRUE/FALSE, not 0/1 -> Option D

4. Quick Check:

   Boolean columns need TRUE/FALSE, not 0/1 [OK]

Hint: Boolean needs TRUE/FALSE, not 0/1 [OK]

Common Mistakes:

• Assuming 0 equals FALSE in all SQL dialects
• Ignoring data type of column
• Thinking syntax error causes no rows

5. You want to implement soft delete on a products table. Which SQL statement correctly marks a product as deleted without removing it?

hard

A. INSERT INTO products (product_id, is_deleted) VALUES (10, TRUE);

B. DELETE FROM products WHERE product_id = 10;

C. UPDATE products SET is_deleted = TRUE WHERE product_id = 10;

D. SELECT * FROM products WHERE is_deleted = TRUE;

Solution

1. Step 1: Understand soft delete update

   Soft delete means updating a flag, not deleting the row.

2. Step 2: Analyze each option

   UPDATE products SET is_deleted = TRUE WHERE product_id = 10; updates is_deleted to TRUE for product 10, marking it deleted.

3. Final Answer:

   UPDATE products SET is_deleted = TRUE WHERE product_id = 10; -> Option C

4. Quick Check:

   Soft delete uses UPDATE to mark deleted [OK]

Hint: Use UPDATE to mark is_deleted TRUE [OK]

Common Mistakes:

• Using DELETE instead of UPDATE
• Trying to INSERT to mark deleted
• Using SELECT instead of modifying data