INSERT INTO single row in SQL - Practice Problems & Coding Challenges

Challenge - 5 Problems

❓ query_result

intermediate

What is the result of this INSERT statement?

Consider a table employees with columns id (integer), name (text), and age (integer).
What will be the content of the table after running this query?

INSERT INTO employees (id, name, age) VALUES (1, 'Alice', 30);

SQL

SELECT * FROM employees;

A []

B [{"id": 0, "name": "Alice", "age": 30}]

C [{"id": 1, "name": "Alice", "age": 30}]

D [{"id": 1, "name": null, "age": 30}]

💡 Hint

The INSERT statement adds one row with the specified values.

The INSERT INTO statement adds a single row with id=1, name='Alice', and age=30 to the employees table.

📝 Syntax

intermediate

Which INSERT statement is syntactically correct?

Given a table products with columns product_id (int), product_name (text), and price (decimal), which of the following INSERT statements will run without syntax errors?

A INSERT INTO products (product_id, product_name, price) VALUES (101, 'Pen', 1.5);

B INSERT products INTO VALUES (101, 'Pen', 1.5);

C INSERT INTO products (product_id, product_name price) VALUES (101, 'Pen', 1.5);

D INSERT INTO products VALUES (101, 'Pen', 1.5);

💡 Hint

Check the order of keywords and commas between column names.

Option D follows the correct syntax: INSERT INTO table VALUES (...). Options A, B, and D have syntax errors such as wrong keyword order, missing commas, or missing parentheses.

❓ optimization

advanced

Which INSERT statement is more efficient for adding a single row?

You want to insert a single row into the orders table with columns order_id, customer, and total. Which option is more efficient and why?

A INSERT INTO orders VALUES (5001, 'John Doe', 250.75);

B INSERT INTO orders (order_id, customer, total) VALUES (5001, 'John Doe', 250.75);

C INSERT INTO orders SELECT 5001, 'John Doe', 250.75;

D INSERT INTO orders SET order_id=5001, customer='John Doe', total=250.75;

💡 Hint

If you provide values for all columns in order, you can omit column names.

Option A is more efficient because it omits column names when all columns are provided in the correct order. Option A is correct but slightly longer. Option A unnecessarily uses SELECT. Option A is MySQL-specific and not standard.

🔧 Debug

advanced

What error does this INSERT statement produce?

Given a table users with columns id (integer, primary key), username (text), and email (text), what error will this statement cause?

INSERT INTO users (id, username) VALUES (1, 'bob');

A Error: Duplicate primary key

B No error, row inserted with email as NULL

C Syntax error: missing value for email

D Error: Column 'email' cannot be null

💡 Hint

If a column is not specified and allows NULL, it defaults to NULL.

Since email is not specified and assuming it allows NULL, the row inserts with email as NULL. No syntax error or duplicate key error occurs.

🧠 Conceptual

expert

What happens if you insert a row with a duplicate primary key?

Consider a table inventory with item_id as the primary key. What is the result of this query?

INSERT INTO inventory (item_id, name) VALUES (10, 'Widget');
INSERT INTO inventory (item_id, name) VALUES (10, 'Gadget');

A Second INSERT fails with a primary key violation error

B Both rows inserted successfully, duplicates allowed

C Second INSERT overwrites the first row

D First INSERT fails because the key is reused

💡 Hint

Primary keys must be unique in a table.

The second INSERT fails because it tries to insert a row with an existing primary key value, violating uniqueness constraints.