UPDATE with RETURNING clause in PostgreSQL - Step-by-Step Execution

Concept Flow - UPDATE with RETURNING clause

Start UPDATE command

↓

Find rows matching WHERE condition

↓

Update specified columns

↓

Collect updated rows

↓

RETURNING clause outputs updated rows

↓

End

The UPDATE command finds rows matching the condition, changes specified columns, then RETURNING outputs the updated rows.

Execution Sample

PostgreSQL

UPDATE employees
SET salary = salary + 500
WHERE department = 'Sales'
RETURNING id, name, salary;

This updates salaries for Sales department employees and returns their id, name, and new salary.

Execution Table

Step	Action	Rows Matched	Columns Updated	RETURNING Output
1	Start UPDATE	-	-	-
2	Find rows WHERE department = 'Sales'	Rows with dept='Sales' found: 2	-	-
3	Update salary = salary + 500	2 rows	salary column updated	-
4	RETURNING id, name, salary	2 rows	-	[{"id": 3, "name": "Alice", "salary": 3500}, {"id": 5, "name": "Bob", "salary": 4200}]
5	End	-	-	-

💡 All matching rows updated and their new values returned by RETURNING clause.

Variable Tracker

Variable	Start	After Step 3	Final
salary of Alice	3000	3500	3500
salary of Bob	3700	4200	4200

Key Moments - 2 Insights

Why do we see output rows after UPDATE when normally UPDATE returns only count?

Because of the RETURNING clause (see execution_table step 4), the updated rows are output instead of just a count.

Does RETURNING show old or new values?

RETURNING shows the new updated values after the change (execution_table step 4 shows updated salaries).

Visual Quiz - 3 Questions

Look at the execution_table at step 2, how many rows matched the WHERE condition?

A 2

B 3

C 0

D 5

💡 Hint

Check the 'Rows Matched' column at step 2 in execution_table.

At which step does the salary column get updated?

A Step 2

B Step 3

C Step 4

D Step 5

💡 Hint

Look at the 'Columns Updated' column in execution_table.

If we remove RETURNING clause, what changes in the output?

A No rows are updated

B Updated rows are still returned

C Only count of updated rows is returned

D Query will fail

💡 Hint

RETURNING clause controls output; without it, UPDATE returns count only.

Concept Snapshot

UPDATE table_name
SET column = value
WHERE condition
RETURNING columns;

- Updates rows matching condition
- RETURNING outputs updated rows
- Useful to see new values immediately

Full Transcript

The UPDATE with RETURNING clause in PostgreSQL first finds rows matching the WHERE condition. Then it updates the specified columns in those rows. After updating, the RETURNING clause outputs the updated rows with the columns requested. This lets you see the new values right away instead of just the count of updated rows. For example, updating salaries in the Sales department and returning id, name, and new salary shows exactly which rows changed and their new data.

Practice

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

easy

A. It returns the updated rows immediately after the update.

B. It deletes the rows after updating them.

C. It creates a backup of the updated rows.

D. It prevents the update from happening.

Solution

1. Step 1: Understand the purpose of UPDATE

   The UPDATE statement changes data in existing rows of a table.

2. Step 2: Role of RETURNING clause

   The RETURNING clause immediately outputs the rows that were updated, showing their new values.

3. Final Answer:

   It returns the updated rows immediately after the update. -> Option A

4. Quick Check:

   RETURNING shows updated rows [OK]

Hint: RETURNING shows updated rows right after update [OK]

Common Mistakes:

• Thinking RETURNING deletes rows
• Assuming RETURNING creates backups
• Believing RETURNING stops the update

2. Which of the following is the correct syntax to update a table and return the updated rows in PostgreSQL?

easy

A. UPDATE table_name SET column1 = value1 WHERE condition RETURNING *;

B. UPDATE table_name SET column1 = value1 RETURN * WHERE condition;

C. UPDATE table_name RETURNING * SET column1 = value1 WHERE condition;

D. UPDATE table_name SET column1 = value1 WHERE condition SHOW RETURNING *;

Solution

1. Step 1: Identify correct UPDATE syntax

   The UPDATE statement must have SET clause before WHERE clause.

2. Step 2: Position of RETURNING clause

   RETURNING clause comes after WHERE clause to output updated rows.

3. Final Answer:

   UPDATE table_name SET column1 = value1 WHERE condition RETURNING *; -> Option A

4. Quick Check:

   RETURNING follows WHERE in UPDATE [OK]

Hint: RETURNING always comes after WHERE clause [OK]

Common Mistakes:

• Placing RETURNING before SET clause
• Using SHOW RETURNING which is invalid
• Putting RETURNING between SET and WHERE

3. Given the table employees with columns id, salary, and department, what will this query return?

UPDATE employees SET salary = salary + 500 WHERE department = 'Sales' RETURNING id, salary;

medium

A. Only the number of rows updated, no data returned.

B. All employees' ids and salaries regardless of department.

C. All employees' ids and new salaries in the Sales department after the raise.

D. An error because RETURNING cannot specify columns.

Solution

1. Step 1: Understand the UPDATE condition

   The query updates salary by adding 500 only for employees in the Sales department.

2. Step 2: Effect of RETURNING clause

   RETURNING id, salary outputs the id and updated salary of only those employees updated.

3. Final Answer:

   All employees' ids and new salaries in the Sales department after the raise. -> Option C

4. Quick Check:

   RETURNING outputs updated rows only [OK]

Hint: RETURNING shows only updated rows, not all rows [OK]

Common Mistakes:

• Thinking all rows are returned
• Expecting only count of updated rows
• Believing RETURNING cannot specify columns

4. What is wrong with this query?

UPDATE products RETURNING * SET price = price * 1.1 WHERE category = 'Books';

medium

A. The price calculation is invalid syntax.

B. The RETURNING clause is placed before SET, causing a syntax error.

C. The WHERE clause is missing.

D. RETURNING cannot be used with UPDATE.

Solution

1. Step 1: Check clause order in UPDATE

   UPDATE syntax requires SET before WHERE and RETURNING last.

2. Step 2: Identify error in query

   RETURNING appears before SET, which is invalid and causes syntax error.

3. Final Answer:

   The RETURNING clause is placed before SET, causing a syntax error. -> Option B

4. Quick Check:

   RETURNING must come after WHERE and SET [OK]

Hint: RETURNING always comes last after WHERE [OK]

Common Mistakes:

• Placing RETURNING before SET
• Omitting WHERE clause when needed
• Misordering clauses in UPDATE

5. You want to increase the salary by 10% for employees in the 'Engineering' department and immediately get their id, old_salary, and new_salary. Which query correctly does this using UPDATE with RETURNING?

hard

A. UPDATE employees SET salary = salary * 1.1 WHERE department = 'Engineering' RETURNING id, salary, salary / 1.1 AS old_salary;

B. UPDATE employees SET salary = salary * 1.1 WHERE department = 'Engineering' RETURNING id, salary, salary * 1.1 AS old_salary;

C. UPDATE employees SET salary = salary * 1.1 WHERE department = 'Engineering' RETURNING id, salary AS old_salary, salary * 1.1 AS new_salary;

D. UPDATE employees SET salary = salary * 1.1 WHERE department = 'Engineering' RETURNING id, salary AS new_salary, salary / 1.1 AS old_salary;

Solution

1. Step 1: Understand the salary update

   Salary is multiplied by 1.1 to increase by 10%, so new salary is salary * 1.1.

2. Step 2: Calculate old salary in RETURNING

   After update, salary column shows new salary. To get old salary, divide new salary by 1.1.

3. Step 3: Check aliasing in RETURNING

   RETURNING must show id, new_salary (salary), and old_salary (salary / 1.1) with correct aliases.

4. Final Answer:

   UPDATE employees SET salary = salary * 1.1 WHERE department = 'Engineering' RETURNING id, salary AS new_salary, salary / 1.1 AS old_salary; -> Option D

5. Quick Check:

   Old salary = new salary / 1.1 [OK]

Hint: Use RETURNING with expressions and aliases for old and new values [OK]

Common Mistakes:

• Confusing old and new salary calculations
• Wrong aliasing in RETURNING clause
• Using expressions incorrectly in RETURNING