INSERT with RETURNING clause in PostgreSQL - Cheat Sheet & Quick Revision

Recall & Review

beginner

What does the RETURNING clause do in a PostgreSQL INSERT statement?

The RETURNING clause returns specified columns from the newly inserted row(s) immediately after the INSERT operation, allowing you to see the inserted data without running a separate query.

beginner

Write a simple INSERT statement with a RETURNING clause to insert a new user with name 'Alice' and return the generated user ID.

Example:
INSERT INTO users (name) VALUES ('Alice') RETURNING id;
This inserts a new user named Alice and returns the new user's ID.

intermediate

Can the RETURNING clause return multiple columns? If yes, how?

Yes, you can return multiple columns by listing them separated by commas. For example:
RETURNING id, name, created_at;
This returns the ID, name, and creation timestamp of the inserted row.

intermediate

Why is using RETURNING better than running a separate SELECT after an INSERT?

Using RETURNING is faster and safer because it gets the inserted data in one step. It avoids race conditions where the data might change between the INSERT and a separate SELECT.

beginner

What happens if you use RETURNING * in an INSERT statement?

The RETURNING * clause returns all columns of the newly inserted row(s). This is useful when you want to see every detail of the inserted data without listing columns individually.

What does the RETURNING clause do in a PostgreSQL INSERT statement?

A Deletes rows after insertion

B Creates a new table

C Updates existing rows

D Returns specified columns from the inserted row(s)

The RETURNING clause returns specified columns from the newly inserted rows.

Which of the following is a valid use of RETURNING in an INSERT?

A INSERT INTO users (name) VALUES ('Bob') WHERE id = 1;

B INSERT INTO users (name) VALUES ('Bob') RETURNING id;

C INSERT INTO users (name) RETURNING id VALUES ('Bob');

D INSERT RETURNING id INTO users VALUES ('Bob');

Option B correctly uses RETURNING after the VALUES clause.

Can RETURNING return multiple columns?

A Yes, by listing columns separated by commas

B No, only one column is allowed

C Only if the table has one column

D Only with <code>SELECT</code> statements

You can return multiple columns by listing them separated by commas in the RETURNING clause.

What is a benefit of using RETURNING instead of a separate SELECT after INSERT?

A It locks the entire table

B It deletes the inserted row automatically

C It avoids race conditions and is more efficient

D It requires more queries

Using RETURNING avoids race conditions and reduces the number of queries.

What does RETURNING * do?

A Returns all columns of the inserted row(s)

B Returns no columns

C Returns only the first column

D Returns the table schema

RETURNING * returns all columns of the inserted row(s).

Explain how the RETURNING clause works in a PostgreSQL INSERT statement and why it is useful.

Think about how you get data back immediately after inserting.

Write an example of an INSERT statement using RETURNING to get the new row's ID and name.

Use a simple table like users with columns id and name.

Practice

1. What does the RETURNING clause do in a PostgreSQL INSERT statement?

easy

A. It creates a backup of the inserted data.

B. It deletes rows after insertion.

C. It updates existing rows instead of inserting.

D. It returns specified columns of the newly inserted rows immediately.

Solution

1. Step 1: Understand the purpose of RETURNING

   The RETURNING clause in PostgreSQL is used to get back specified columns from the rows that were just inserted.

2. Step 2: Compare with other options

   The other options describe actions unrelated to RETURNING. RETURNING does not delete, update, or backup data.

3. Final Answer:

   It returns specified columns of the newly inserted rows immediately. -> Option D

4. Quick Check:

   RETURNING returns inserted data [OK]

Hint: RETURNING fetches inserted row data instantly [OK]

Common Mistakes:

• Thinking RETURNING deletes or updates data
• Confusing RETURNING with SELECT
• Assuming RETURNING creates backups

2. Which of the following is the correct syntax to insert a row and return the generated id in PostgreSQL?

easy

A. INSERT INTO users VALUES ('Alice') RETURNING id;

B. INSERT INTO users (name) RETURN id VALUES ('Alice');

C. INSERT INTO users (name) VALUES ('Alice') RETURNING id;

D. INSERT INTO users (name) VALUES ('Alice') RETURN id;

Solution

1. Step 1: Check correct RETURNING syntax

   The correct syntax places RETURNING after VALUES and specifies the column to return, like RETURNING id.

2. Step 2: Validate each option

   INSERT INTO users (name) VALUES ('Alice') RETURNING id; matches the correct syntax. Placing RETURNING before VALUES or using RETURN instead of RETURNING is incorrect. INSERT INTO users VALUES ('Alice') RETURNING id; misses column list before VALUES.

3. Final Answer:

   INSERT INTO users (name) VALUES ('Alice') RETURNING id; -> Option C

4. Quick Check:

   RETURNING follows VALUES with column list [OK]

Hint: RETURNING goes right after VALUES clause [OK]

Common Mistakes:

• Placing RETURNING before VALUES
• Omitting column list in INSERT
• Using RETURN instead of RETURNING

3. Given the table products(id SERIAL PRIMARY KEY, name TEXT, price NUMERIC), what will this query return?

INSERT INTO products (name, price) VALUES ('Pen', 1.5) RETURNING id, price;

medium

A. The new product's id and price, e.g., (5, 1.5)

B. Only the id of the new product

C. An error because RETURNING can't return multiple columns

D. Nothing, INSERT does not return rows

Solution

1. Step 1: Understand RETURNING with multiple columns

   RETURNING can return one or more columns from the inserted row(s). Here, id and price are requested.

2. Step 2: Predict output

   The query inserts a new product and returns its auto-generated id and the price 1.5 as a row, e.g., (5, 1.5).

3. Final Answer:

   The new product's id and price, e.g., (5, 1.5) -> Option A

4. Quick Check:

   RETURNING multiple columns returns all requested [OK]

Hint: RETURNING can list multiple columns separated by commas [OK]

Common Mistakes:

• Assuming RETURNING returns only one column
• Expecting no output from INSERT
• Thinking RETURNING causes syntax error with multiple columns

4. What is wrong with this query?

INSERT INTO orders (product_id, quantity) VALUES (10, 3) RETURNING;

medium

A. VALUES clause is incorrectly formatted.

B. RETURNING clause is missing column names to return.

C. INSERT statement cannot have RETURNING clause.

D. product_id and quantity columns do not exist.

Solution

1. Step 1: Check RETURNING syntax

   RETURNING must specify at least one column or * to return. Here, it is empty, which is invalid syntax.

2. Step 2: Verify other parts

   VALUES clause and columns look correct. INSERT supports RETURNING. Assuming columns exist, no error there.

3. Final Answer:

   RETURNING clause is missing column names to return. -> Option B

4. Quick Check:

   RETURNING needs columns or * [OK]

Hint: RETURNING must specify columns or * [OK]

Common Mistakes:

• Leaving RETURNING empty
• Confusing RETURNING with WHERE
• Assuming RETURNING is optional but empty

5. You want to insert multiple rows into employees(name, department) and get back their generated id values. Which query correctly does this and returns all new ids?

hard

A. INSERT INTO employees (name, department) VALUES ('John', 'HR'), ('Jane', 'IT') RETURNING id;

B. INSERT INTO employees (name, department) RETURNING id VALUES ('John', 'HR'), ('Jane', 'IT');

C. INSERT INTO employees (name, department) VALUES ('John', 'HR'); RETURNING id; INSERT INTO employees (name, department) VALUES ('Jane', 'IT'); RETURNING id;

D. INSERT INTO employees (name, department) VALUES ('John', 'HR'), ('Jane', 'IT') RETURN id;

Solution

1. Step 1: Understand multi-row INSERT with RETURNING

   PostgreSQL allows inserting multiple rows in one statement and RETURNING returns all inserted rows' specified columns.

2. Step 2: Analyze each option

   INSERT INTO employees (name, department) VALUES ('John', 'HR'), ('Jane', 'IT') RETURNING id; correctly inserts two rows and returns their ids. INSERT INTO employees (name, department) RETURNING id VALUES ('John', 'HR'), ('Jane', 'IT'); misplaces RETURNING before VALUES. INSERT INTO employees (name, department) VALUES ('John', 'HR'); RETURNING id; INSERT INTO employees (name, department) VALUES ('Jane', 'IT'); RETURNING id; splits inserts and RETURNING incorrectly. INSERT INTO employees (name, department) VALUES ('John', 'HR'), ('Jane', 'IT') RETURN id; uses invalid RETURN keyword.

3. Final Answer:

   INSERT INTO employees (name, department) VALUES ('John', 'HR'), ('Jane', 'IT') RETURNING id; -> Option A

4. Quick Check:

   Multi-row INSERT with RETURNING returns all rows [OK]

Hint: Use RETURNING after multi-row VALUES to get all ids [OK]

Common Mistakes:

• Placing RETURNING before VALUES
• Splitting inserts instead of multi-row insert
• Using RETURN instead of RETURNING