Returning modified rows with RETURNING in PostgreSQL - Cheat Sheet & Quick Revision

Recall & Review

beginner

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

It returns the rows that were modified by the UPDATE, showing their new values immediately after the change.

beginner

How can RETURNING help when you want to see the new values of rows after an INSERT?

RETURNING lets you get the inserted rows' data right away without running a separate SELECT query.

intermediate

Can RETURNING be used with DELETE statements in PostgreSQL? What does it return?

Yes, RETURNING can be used with DELETE to return the rows that were deleted, showing their values before removal.

beginner

Write a simple UPDATE query that changes a user's email and returns the updated row using RETURNING.

UPDATE users SET email = '[e-mail]' WHERE id = 1 RETURNING *;

intermediate

Why is RETURNING useful in applications that modify data?

It saves time and resources by combining data modification and retrieval in one step, avoiding extra queries.

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

A Prevents the update from happening

B Returns the modified rows after the update

C Deletes the rows after updating

D Creates a backup of the table

RETURNING returns the rows that were changed by the UPDATE statement.

Which SQL statements can use RETURNING in PostgreSQL?

A INSERT, UPDATE, DELETE

B SELECT only

C CREATE and DROP

D ALTER only

RETURNING works with INSERT, UPDATE, and DELETE to return affected rows.

What will this query return? UPDATE products SET price = price * 1.1 RETURNING id, price;

A Only the old prices before update

B Nothing, it only updates

C The id and new price of all updated products

D An error because RETURNING is invalid here

RETURNING returns the specified columns of updated rows with new values.

Why might RETURNING improve application performance?

A It combines update and retrieval in one query

B It caches data automatically

C It compresses the database

D It disables logging

RETURNING avoids extra SELECT queries by returning data immediately after modification.

What happens if you use RETURNING * in a DELETE statement?

A It causes a syntax error

B It returns nothing

C It returns the rows after deletion

D It returns all columns of the deleted rows

RETURNING * returns all columns of rows before they are deleted.

Explain how the RETURNING clause works in PostgreSQL and give an example of its use in an UPDATE statement.

Think about how to get updated rows back immediately.

Describe the benefits of using RETURNING in data modification queries in PostgreSQL.

Consider what happens without RETURNING and why it matters.

Practice

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

easy

A. It delays the update until a commit is issued.

B. It prevents the update from modifying any rows.

C. It returns the rows that were updated immediately after the update.

D. It returns the number of rows in the table before the update.

Solution

1. Step 1: Understand the purpose of RETURNING

   The RETURNING clause is used to get the data of rows affected by an INSERT, UPDATE, or DELETE immediately.

2. Step 2: Apply to UPDATE statement

   When used with UPDATE, RETURNING shows the updated rows without needing a separate SELECT query.

3. Final Answer:

   It returns the rows that were updated immediately after the update. -> Option C

4. Quick Check:

   RETURNING shows changed rows = B [OK]

Hint: RETURNING shows changed rows right after modification [OK]

Common Mistakes:

• Thinking RETURNING delays changes
• Assuming RETURNING prevents updates
• Confusing RETURNING with row count only

2. Which of the following is the correct syntax to return all columns of updated rows in PostgreSQL?

easy

A. UPDATE table_name SET col = val RETURNING ALL COLUMNS;

B. UPDATE table_name SET col = val RETURNING *;

C. UPDATE table_name SET col = val RETURNING ALL;

D. UPDATE table_name SET col = val RETURN *;

Solution

1. Step 1: Recall correct RETURNING syntax

   PostgreSQL uses RETURNING followed by column names or * to return all columns.

2. Step 2: Identify correct option

   Only UPDATE table_name SET col = val RETURNING *; uses RETURNING * which is valid syntax to return all columns.

3. Final Answer:

   UPDATE table_name SET col = val RETURNING *; -> Option B

4. Quick Check:

   RETURNING * returns all columns [OK]

Hint: Use RETURNING * to get all columns after update [OK]

Common Mistakes:

• Using RETURN instead of RETURNING
• Writing RETURNING ALL instead of RETURNING *
• Adding extra keywords like ALL COLUMNS

3. Given the table users(id INT, name TEXT, age INT) with rows:
(1, 'Alice', 30), (2, 'Bob', 25)
What will this query return?

UPDATE users SET age = age + 1 WHERE id = 2 RETURNING id, age;

medium

A. (2, 26)

B. (2, 25)

C. (1, 31)

D. (1, 30)

Solution

1. Step 1: Identify updated row

   The WHERE clause updates only the row with id = 2 (Bob).

2. Step 2: Calculate new age and returned columns

   Bob's age increases from 25 to 26. RETURNING id, age returns (2, 26).

3. Final Answer:

   (2, 26) -> Option A

4. Quick Check:

   Updated row with id=2 returns new age 26 [OK]

Hint: RETURNING shows updated values immediately [OK]

Common Mistakes:

• Returning old values instead of updated
• Confusing which row is updated
• Ignoring WHERE clause effect

4. What is wrong with this query?

UPDATE products SET price = price * 1.1 RETURNING;

medium

A. RETURNING cannot be used with UPDATE statements.

B. The multiplication operator * is invalid in UPDATE.

C. Missing WHERE clause causes syntax error.

D. RETURNING clause requires columns or * to specify what to return.

Solution

1. Step 1: Check RETURNING syntax

   RETURNING must be followed by column names or *; empty RETURNING is invalid syntax.

2. Step 2: Validate other parts

   Multiplication and UPDATE without WHERE are valid; RETURNING with no columns is the error.

3. Final Answer:

   RETURNING clause requires columns or * to specify what to return. -> Option D

4. Quick Check:

   RETURNING needs columns or * [OK]

Hint: Always specify columns or * after RETURNING [OK]

Common Mistakes:

• Leaving RETURNING empty
• Thinking WHERE is mandatory for syntax
• Believing RETURNING disallowed in UPDATE

5. You want to increase the salary by 10% for employees in department 5 and get their id and new salary. Which query correctly does this and returns the updated rows?

hard

A. UPDATE employees SET salary = salary * 1.1 WHERE department_id = 5 RETURNING id, salary;

B. UPDATE employees SET salary = salary + 10 WHERE department_id = 5 RETURNING *;

C. UPDATE employees SET salary = salary * 1.1 RETURNING id, salary WHERE department_id = 5;

D. UPDATE employees SET salary = salary * 1.1 WHERE department_id = 5 RETURN id, salary;

Solution

1. Step 1: Identify correct UPDATE with WHERE and RETURNING

   The query must update only department 5 employees and return id and salary.

2. Step 2: Check syntax correctness

   UPDATE employees SET salary = salary * 1.1 WHERE department_id = 5 RETURNING id, salary; uses correct syntax: UPDATE ... SET ... WHERE ... RETURNING id, salary;

3. Step 3: Eliminate incorrect options

   Adding a fixed 10 instead of multiplying by 1.1 doesn't implement a 10% increase. Placing RETURNING before WHERE is invalid syntax. Using RETURN instead of RETURNING is wrong.

4. Final Answer:

   UPDATE employees SET salary = salary * 1.1 WHERE department_id = 5 RETURNING id, salary; -> Option A

5. Quick Check:

   Correct syntax with WHERE and RETURNING columns [OK]

Hint: RETURNING follows WHERE clause with columns listed [OK]

Common Mistakes:

• Placing RETURNING before WHERE
• Using RETURN instead of RETURNING
• Adding fixed amount instead of percentage