UPDATE with RETURNING clause in PostgreSQL - Interactive Code Practice

Practice - 5 Tasks

1fill in blank

easy

Complete the code to update the salary of employees in the 'employees' table.

PostgreSQL

UPDATE employees SET salary = salary [1] 1000 WHERE department = 'Sales';

Drag options to blanks, or click blank then click option'

A+

B-

C*

D/

Attempts:

3 left

💡 Hint

Common Mistakes

Using '-' will decrease the salary instead of increasing it.

Using '*' or '/' will multiply or divide the salary, which is not intended here.

The '+' operator increases the salary by 1000 for employees in the Sales department.

2fill in blank

medium

Complete the code to return the updated rows after increasing the salary.

PostgreSQL

UPDATE employees SET salary = salary + 500 WHERE id = 10 [1] salary, id;

Drag options to blanks, or click blank then click option'

ARETURNING

BRETURN

COUTPUT

DSELECT

Attempts:

3 left

💡 Hint

Common Mistakes

Using 'RETURN' alone is not valid SQL syntax here.

Using 'OUTPUT' is a SQL Server syntax, not PostgreSQL.

Using 'SELECT' after UPDATE is incorrect.

The 'RETURNING' clause in PostgreSQL returns the specified columns of the updated rows.

3fill in blank

hard

Fix the error in the code to correctly update and return the employee's name and new salary.

PostgreSQL

UPDATE employees SET salary = salary + 200 WHERE id = 5 RETURNING [1];

Drag options to blanks, or click blank then click option'

Aname; salary

Bname salary

Cname, salary

Dname salary,

Attempts:

3 left

💡 Hint

Common Mistakes

Leaving out commas between column names.

Adding semicolons inside the RETURNING clause.

Column names in RETURNING must be separated by commas without extra characters.

4fill in blank

hard

Fill both blanks to update the 'status' and return the 'id' and 'status' of updated rows.

PostgreSQL

UPDATE orders SET status = [1] WHERE shipped = false RETURNING [2], status;

Drag options to blanks, or click blank then click option'

A'shipped'

Bid

Corder_id

D'delivered'

Attempts:

3 left

💡 Hint

Common Mistakes

Not using quotes around string values in the SET clause.

Returning a column that does not exist or is not relevant.

The status is set to 'delivered' (a string), and the 'id' column is returned along with status.

5fill in blank

hard

Fill all three blanks to update 'quantity', return 'order_id', 'quantity', and only rows where quantity is greater than 10.

PostgreSQL

UPDATE order_items SET quantity = quantity - [1] WHERE quantity > [2] RETURNING [3], quantity;

Drag options to blanks, or click blank then click option'

A5

B10

Corder_id

D1

Attempts:

3 left

💡 Hint

Common Mistakes

Using wrong numbers for subtraction or filtering.

Returning a column name that does not exist.

Decrease quantity by 5, filter rows where quantity > 10, and return 'order_id' and updated quantity.

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