DELETE vs TRUNCATE behavior in SQL - Interactive Practice

Practice - 5 Tasks

1fill in blank

easy

Complete the code to delete all rows from the table named 'employees'.

SQL

DELETE FROM [1];

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

Aemployee

Bemp

Cemployees

Dstaff

Attempts:

3 left

💡 Hint

Common Mistakes

Using a wrong table name like 'employee' or 'emp'.

Forgetting the semicolon at the end.

The correct table name is 'employees'. This command deletes all rows from that table.

2fill in blank

medium

Complete the code to remove all rows quickly from the table named 'orders' without logging individual row deletions.

SQL

TRUNCATE TABLE [1];

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

Aorders

Border_table

Corder_list

Dorder

Attempts:

3 left

💡 Hint

Common Mistakes

Using singular form 'order' instead of 'orders'.

Confusing TRUNCATE with DELETE syntax.

TRUNCATE TABLE orders removes all rows quickly and resets storage without logging each row deletion.

3fill in blank

hard

Fix the error in the command to delete rows from 'customers' where the city is 'Paris'.

SQL

DELETE FROM customers WHERE city [1] 'Paris';

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

A===

B==

Cequals

D=

Attempts:

3 left

💡 Hint

Common Mistakes

Using '==' or '===' instead of '='.

Writing 'equals' as a word instead of '='.

In SQL, the equality operator is '='. Using '==' or '===' causes syntax errors.

4fill in blank

hard

Fill both blanks to write a command that deletes all rows from 'products' but logs each deletion.

SQL

DELETE FROM [1] WHERE [2];

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

Aproducts

B1=1

CTRUE

D0=0

Attempts:

3 left

💡 Hint

Common Mistakes

Using TRUNCATE instead of DELETE for logging.

Using a false condition in WHERE clause.

DELETE FROM products WHERE 1=1 deletes all rows and logs each deletion. '1=1' is always true.

5fill in blank

hard

Fill the blanks to write a command that truncates the 'logs' table and resets identity counters.

SQL

TRUNCATE TABLE [1] [2] RESTART IDENTITY;

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

Alogs

BCASCADE

CONLY

DIF EXISTS

Attempts:

3 left

💡 Hint

Common Mistakes

Omitting CASCADE when dependent tables exist.

Forgetting RESTART IDENTITY.

TRUNCATE TABLE logs CASCADE RESTART IDENTITY; truncates logs, resets IDs, and cascades to dependent tables.

Practice

1. Which statement correctly describes the difference between DELETE and TRUNCATE in SQL?

easy

A. TRUNCATE is slower than DELETE because it logs each row removal.

B. TRUNCATE removes rows one by one and can use a WHERE clause; DELETE removes all rows quickly without logging each row.

C. DELETE and TRUNCATE both remove rows one by one and support WHERE clauses.

D. DELETE removes rows one by one and can use a WHERE clause; TRUNCATE removes all rows quickly without logging each row.

Solution

1. Step 1: Understand DELETE behavior

   DELETE removes rows individually and supports filtering with WHERE.

2. Step 2: Understand TRUNCATE behavior

   TRUNCATE removes all rows quickly without logging each row, and does not support WHERE.

3. Final Answer:

   DELETE removes rows one by one and can use a WHERE clause; TRUNCATE removes all rows quickly without logging each row. -> Option D

4. Quick Check:

   DELETE = selective row removal, TRUNCATE = fast full clear [OK]

Hint: DELETE filters rows; TRUNCATE clears all fast [OK]

Common Mistakes:

• Thinking TRUNCATE supports WHERE clause
• Confusing which command logs each row
• Believing DELETE is faster than TRUNCATE

2. Which of the following is the correct syntax to remove all rows from a table named Employees using TRUNCATE?

easy

A. DELETE FROM Employees;

B. TRUNCATE TABLE Employees;

C. TRUNCATE Employees WHERE id > 10;

D. REMOVE ALL FROM Employees;

Solution

1. Step 1: Recall TRUNCATE syntax

   The correct syntax to remove all rows quickly is TRUNCATE TABLE table_name;.

2. Step 2: Check options for correctness

   DELETE FROM Employees; uses DELETE; REMOVE ALL FROM Employees; is invalid SQL; TRUNCATE Employees WHERE id > 10; incorrectly adds WHERE to TRUNCATE; TRUNCATE TABLE Employees; matches the correct syntax.

3. Final Answer:

   TRUNCATE TABLE Employees; -> Option B

4. Quick Check:

   TRUNCATE syntax = TRUNCATE TABLE [OK]

Hint: TRUNCATE always uses TABLE keyword [OK]

Common Mistakes:

• Adding WHERE clause to TRUNCATE
• Using DELETE syntax for TRUNCATE
• Using non-existent REMOVE command

3. Given a table Orders with 1000 rows, what will be the number of rows after executing DELETE FROM Orders WHERE OrderDate < '2023-01-01'; if 300 rows have OrderDate before 2023?

medium

A. 700 rows remain

B. 0 rows remain

C. 1000 rows remain

D. Syntax error

Solution

1. Step 1: Understand DELETE with WHERE clause

   The DELETE command removes only rows matching the condition: OrderDate < '2023-01-01'.

2. Step 2: Calculate remaining rows

   Since 300 rows match the condition, they are deleted. Remaining rows = 1000 - 300 = 700.

3. Final Answer:

   700 rows remain -> Option A

4. Quick Check:

   1000 - 300 = 700 rows left [OK]

Hint: DELETE with WHERE removes only matching rows [OK]

Common Mistakes:

• Assuming DELETE removes all rows without WHERE
• Confusing DELETE with TRUNCATE behavior
• Thinking syntax error due to date format

4. You run the command TRUNCATE TABLE Customers WHERE Country = 'USA'; but get an error. What is the most likely cause?

medium

A. TRUNCATE does not support WHERE clauses.

B. The table Customers does not exist.

C. TRUNCATE requires a WHERE clause.

D. You must use DELETE instead of TRUNCATE for all tables.

Solution

1. Step 1: Check TRUNCATE command rules

   TRUNCATE removes all rows and does not allow filtering with WHERE.

2. Step 2: Identify error cause

   Using WHERE with TRUNCATE causes a syntax error because TRUNCATE does not support WHERE clauses.

3. Final Answer:

   TRUNCATE does not support WHERE clauses. -> Option A

4. Quick Check:

   TRUNCATE = no WHERE allowed [OK]

Hint: TRUNCATE never uses WHERE clause [OK]

Common Mistakes:

• Assuming TRUNCATE supports WHERE
• Thinking table absence causes this error
• Believing DELETE must always replace TRUNCATE

5. You want to quickly remove all rows from a large table Logs but keep the table structure and reset identity counters. Which command should you use and why?

hard

A. Use DELETE FROM Logs WHERE 1=1; because it is faster than TRUNCATE.

B. Use DELETE FROM Logs; because it removes rows and resets identity counters.

C. Use TRUNCATE TABLE Logs; because it removes all rows fast and resets identity counters.

D. Use DROP TABLE Logs; to remove all rows and keep structure.

Solution

1. Step 1: Identify command for fast full table clearing

   TRUNCATE TABLE removes all rows quickly and resets identity counters.

2. Step 2: Compare with DELETE and DROP

   DELETE removes rows slowly and does not reset identity counters; DROP removes table structure.

3. Final Answer:

   Use TRUNCATE TABLE Logs; because it removes all rows fast and resets identity counters. -> Option C

4. Quick Check:

   TRUNCATE = fast clear + reset identity [OK]

Hint: TRUNCATE clears fast and resets identity counters [OK]

Common Mistakes:

• Thinking DELETE resets identity counters
• Using DROP when structure must be kept
• Believing DELETE is faster than TRUNCATE