Returning modified rows with RETURNING in PostgreSQL - Step-by-Step Execution

Concept Flow - Returning modified rows with RETURNING

Start UPDATE/DELETE/INSERT

↓

Modify rows in table

↓

RETURNING clause activated?

No→No rows returned

Yes↓

Collect modified rows

↓

Return rows to client

When you run an UPDATE, DELETE, or INSERT with RETURNING, the database modifies rows and then sends back the changed rows to you.

Execution Sample

PostgreSQL

UPDATE employees
SET salary = salary * 1.1
WHERE department = 'Sales'
RETURNING id, salary;

This query increases salary by 10% for Sales department employees and returns their id and new salary.

Execution Table

Step	Row ID	Original Salary	Condition (department='Sales')	Action	Returned Row
1	101	50000	True	Salary updated to 55000	id=101, salary=55000
2	102	48000	False	No change	No
3	103	52000	True	Salary updated to 57200	id=103, salary=57200
4	104	47000	False	No change	No
5	105	51000	True	Salary updated to 56100	id=105, salary=56100
6	-	-	-	-	Execution ends: all rows checked

💡 All rows processed; only rows matching condition updated and returned.

Variable Tracker

Variable	Start	After 1	After 2	After 3	Final
salary for id=101	50000	55000	55000	55000	55000
salary for id=102	48000	48000	48000	48000	48000
salary for id=103	52000	52000	57200	57200	57200
salary for id=104	47000	47000	47000	47000	47000
salary for id=105	51000	51000	51000	56100	56100

Key Moments - 2 Insights

Why do some rows not appear in the RETURNING output even though they exist in the table?

Only rows that meet the WHERE condition and are modified by the UPDATE appear in RETURNING, as shown in execution_table rows 2 and 4 where condition is False and no rows are returned.

Does RETURNING show the old values or the new updated values?

RETURNING shows the new updated values after the modification, as seen in execution_table rows 1, 3, and 5 where salaries are increased.

Visual Quiz - 3 Questions

Look at the execution_table, what is the salary of employee with id=103 after the update?

A 5200

B 52000

C 57200

D None

💡 Hint

Check the 'Returned Row' and 'Action' columns for row 3 in execution_table.

At which step does the condition department='Sales' become false?

A Step 2

B Step 3

C Step 1

D Step 5

💡 Hint

Look at the 'Condition' column in execution_table rows to find where it is False.

If the RETURNING clause was removed, what would change in the execution?

A Modified rows would still be returned

B No rows would be returned after update

C The update would not happen

D Only the first row would be returned

💡 Hint

RETURNING controls what rows are sent back; without it, no rows are returned.

Concept Snapshot

UPDATE/DELETE/INSERT with RETURNING
modifies rows then returns those rows
RETURNING shows new values after change
Only modified rows matching condition return
Useful to get updated data immediately

Full Transcript

This visual execution shows how PostgreSQL processes an UPDATE with RETURNING. First, it checks each row in the table. If the row matches the condition (department='Sales'), it updates the salary by 10%. Then, because of RETURNING, it sends back the id and new salary of those updated rows. Rows not matching the condition are not changed and not returned. The variable tracker shows salary changes step by step. Key moments clarify why only some rows return and that RETURNING shows new values. The quiz tests understanding of these steps.

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