INSERT with DEFAULT values in SQL - Cheat Sheet & Quick Revision

Recall & Review

beginner

What does the SQL statement INSERT INTO table_name DEFAULT VALUES; do?

It inserts a new row into table_name using all the default values defined for the columns. No specific values are provided.

intermediate

Can you use INSERT INTO table_name DEFAULT VALUES; if the table has columns without default values and no NULL allowed?

No. If a column does not have a default value and does not allow NULL, the insert will fail because the database doesn't know what value to put.

beginner

How do you insert a row with default values for some columns and specific values for others?

You specify the columns and values you want, and omit the others. The omitted columns will use their default values if defined.

beginner

Why might using INSERT with DEFAULT VALUES be useful in real life?

It is useful when you want to add a new row but rely on the database to fill in standard values like timestamps, auto-increment IDs, or default status flags.

intermediate

What happens if you try INSERT INTO table_name DEFAULT VALUES; on a table with no default values at all?

The insert will fail if any column requires a value and has no default or allows NULL. Otherwise, it inserts a row with NULLs where allowed.

What does INSERT INTO users DEFAULT VALUES; do?

A Updates existing rows with default values

B Deletes all rows from the users table

C Inserts a new row with all columns set to their default values

D Returns an error always

This statement inserts a new row using the default values defined for each column.

If a column has no default and does not allow NULL, what happens when you use INSERT DEFAULT VALUES?

A The database assigns a default value automatically

B The insert succeeds with NULL in that column

C The column gets a random value

D The insert fails with an error

The insert fails because the database requires a value but none is provided.

How can you insert a row with some columns using default values and others with specific values?

A Use <code>INSERT INTO table (col1, col2) VALUES (val1, DEFAULT);</code>

B Use <code>INSERT INTO table DEFAULT VALUES;</code> and then update

C You cannot mix default and specific values in one insert

D Use <code>UPDATE</code> instead of <code>INSERT</code>

You can specify DEFAULT for columns in the VALUES list to use their default values.

Which of these is a valid reason to use INSERT with DEFAULT VALUES?

A To delete all rows in a table

B To quickly add a row with system-generated values like timestamps

C To update existing rows with default values

D To select rows with default values

It allows inserting rows that rely on default column values such as auto-generated timestamps.

What is required for INSERT DEFAULT VALUES to work without error?

A All columns must have default values or allow NULL

B At least one column must have a default value

C The table must be empty

D The table must have a primary key

If any column requires a value and has no default or NULL allowed, the insert will fail.

Explain how INSERT with DEFAULT VALUES works and when you would use it.

Think about adding a new record without specifying any data.

What happens if you try to insert default values into a table with columns that have no defaults and do not allow NULL?

Consider what the database needs to store a valid row.

Practice

1. What does the SQL statement INSERT INTO table_name DEFAULT VALUES; do?

easy

A. Inserts a new row using all default values for columns

B. Deletes all rows from the table

C. Updates existing rows with default values

D. Selects all rows with default values

Solution

1. Step 1: Understand the INSERT statement

   The statement inserts a new row into the table.

2. Step 2: Recognize DEFAULT VALUES usage

   Using DEFAULT VALUES means the new row uses default values defined for each column.

3. Final Answer:

   Inserts a new row using all default values for columns -> Option A

4. Quick Check:

   INSERT ... DEFAULT VALUES inserts default row [OK]

Hint: DEFAULT VALUES inserts a row with all default column values [OK]

Common Mistakes:

• Thinking it deletes or updates rows
• Confusing DEFAULT VALUES with SELECT
• Assuming it inserts NULLs instead of defaults

2. Which of the following is the correct syntax to insert a row with default values in SQL?

easy

A. INSERT INTO table_name VALUES (DEFAULT);

B. INSERT INTO table_name VALUES DEFAULT;

C. INSERT DEFAULT INTO table_name VALUES;

D. INSERT INTO table_name DEFAULT VALUES;

Solution

1. Step 1: Recall correct syntax for default insertion

   The correct syntax is INSERT INTO table_name DEFAULT VALUES; to insert a row with all default values.

2. Step 2: Check each option

   INSERT INTO table_name DEFAULT VALUES; matches the correct syntax exactly; others are invalid or incorrect.

3. Final Answer:

   INSERT INTO table_name DEFAULT VALUES; -> Option D

4. Quick Check:

   Correct syntax = INSERT INTO ... DEFAULT VALUES [OK]

Hint: Remember: DEFAULT VALUES comes after table name in INSERT [OK]

Common Mistakes:

• Placing DEFAULT inside VALUES parentheses
• Swapping DEFAULT and VALUES keywords
• Using incorrect keyword order

3. Given the table users(id INT DEFAULT 0, name VARCHAR(20) DEFAULT 'guest'), what will be the result of INSERT INTO users DEFAULT VALUES; SELECT * FROM users; after running on an empty table?

medium

A. Empty result set

B. [{"id": 0, "name": "guest"}]

C. Syntax error

D. [{"id": NULL, "name": NULL}]

Solution

1. Step 1: Understand table defaults

   The table has default values: id = 0, name = 'guest'.

2. Step 2: Effect of INSERT DEFAULT VALUES

   Inserting default values adds a row with id=0 and name='guest'.

3. Step 3: SELECT result

   After insertion, selecting all rows returns one row with those default values.

4. Final Answer:

   [{"id": 0, "name": "guest"}] -> Option B

5. Quick Check:

   Defaults inserted row = id 0, name guest [OK]

Hint: Defaults fill columns if no values given [OK]

Common Mistakes:

• Expecting NULL instead of default values
• Assuming syntax error due to DEFAULT VALUES
• Thinking table remains empty

4. Consider the table products(id INT NOT NULL, name VARCHAR(20) DEFAULT 'unknown'). What error occurs when running INSERT INTO products DEFAULT VALUES;?

medium

A. Error: Column 'id' has no default and no value provided

B. No error, inserts row with NULL id and 'unknown' name

C. Syntax error due to DEFAULT VALUES usage

D. Inserts row with id=0 and name='unknown'

Solution

1. Step 1: Check columns for defaults

   The 'id' column has no default and is NOT nullable.

2. Step 2: Effect of INSERT DEFAULT VALUES

   Trying to insert default values fails because 'id' has no default and no value is given.

3. Final Answer:

   Error: Column 'id' has no default and no value provided -> Option A

4. Quick Check:

   Missing default for NOT NULL column causes error [OK]

Hint: All columns need defaults or allow NULL for DEFAULT VALUES [OK]

Common Mistakes:

• Assuming NULL is inserted automatically
• Thinking DEFAULT VALUES always works
• Confusing syntax error with constraint error

5. You have a table orders(order_id INT PRIMARY KEY DEFAULT nextval('order_seq'), status VARCHAR(10) DEFAULT 'pending', created_at TIMESTAMP DEFAULT CURRENT_TIMESTAMP). Which SQL statement correctly inserts a new order using all defaults except setting status to 'shipped'?

hard

A. INSERT INTO orders (order_id, status, created_at) VALUES (DEFAULT, DEFAULT, 'shipped');

B. INSERT INTO orders DEFAULT VALUES SET status = 'shipped';

C. INSERT INTO orders (status) VALUES ('shipped');

D. INSERT INTO orders (DEFAULT, 'shipped', DEFAULT);

Solution

1. Step 1: Understand default and explicit values

   We want to use defaults for order_id and created_at, but set status explicitly.

2. Step 2: Check each option

   INSERT INTO orders (status) VALUES ('shipped'); correctly lets the DBMS use defaults implicitly for unspecified columns order_id and created_at. INSERT INTO orders DEFAULT VALUES SET status = 'shipped'; is invalid syntax. INSERT INTO orders (order_id, status, created_at) VALUES (DEFAULT, DEFAULT, 'shipped'); incorrectly sets status to its default ('pending') and attempts to set created_at to 'shipped' causing a type mismatch error. INSERT INTO orders (DEFAULT, 'shipped', DEFAULT); is invalid syntax (missing VALUES keyword).

3. Final Answer:

   INSERT INTO orders (status) VALUES ('shipped'); -> Option C

4. Quick Check:

   Unspecified columns use their default values automatically [OK]

Hint: Unspecified columns in INSERT use column defaults [OK]

Common Mistakes:

• Thinking omitting columns always causes errors
• Using DEFAULT VALUES with SET syntax
• Misplacing values and DEFAULT keywords in VALUES clause