DELETE without WHERE (danger) in SQL - Practice Problems & Coding Challenges

Challenge - 5 Problems

❓ query_result

intermediate

What is the result of this DELETE query?

Consider a table Employees with 5 rows. What happens after running this SQL command?

DELETE FROM Employees;

SQL

DELETE FROM Employees;

A All 5 rows in Employees are deleted.

B Only rows matching a condition are deleted.

C No rows are deleted because WHERE clause is missing.

D Syntax error because WHERE clause is required.

💡 Hint

Think about what happens if you don't specify any condition in DELETE.

Without a WHERE clause, DELETE removes all rows from the table.

🧠 Conceptual

intermediate

Why is DELETE without WHERE dangerous?

Which of the following best explains the risk of running DELETE without a WHERE clause?

A It only deletes rows with NULL values.

B It causes a syntax error and stops execution.

C It deletes all rows, possibly causing data loss.

D It locks the table permanently.

💡 Hint

Think about what happens to data when no filter is applied.

DELETE without WHERE removes every row, which can cause unintended data loss.

📝 Syntax

advanced

Which DELETE query deletes only employees older than 30?

Choose the correct DELETE statement that removes only employees older than 30 years.

A DELETE Employees WHERE age > 30;

B DELETE FROM Employees WHERE age > 30;

C DELETE FROM Employees age > 30;

D DELETE * FROM Employees WHERE age > 30;

💡 Hint

Remember the correct syntax for DELETE with a condition.

Option B uses correct DELETE syntax with WHERE clause to filter rows.

🔧 Debug

advanced

What error occurs with this DELETE statement?

Given this query:

DELETE FROM Employees WHERE;

What error will the database return?

SQL

DELETE FROM Employees WHERE;

A Syntax error due to incomplete WHERE clause.

B No rows deleted, query runs successfully.

C Deletes all rows because WHERE is empty.

D Runtime error due to missing table name.

💡 Hint

Check if WHERE clause is complete and valid.

A WHERE clause must have a condition; empty WHERE causes syntax error.

❓ optimization

expert

How to safely delete all rows but keep table structure?

You want to remove all rows from a large table Orders quickly and keep the table structure intact. Which is the best approach?

A Drop and recreate the Orders table.

B Use DELETE FROM Orders WHERE 1=1;

C Use DELETE FROM Orders;

D Use TRUNCATE TABLE Orders;

💡 Hint

Consider performance and preserving table schema.

TRUNCATE is faster than DELETE without WHERE and keeps table structure.