UPDATE multiple columns in SQL - Step-by-Step Execution

Concept Flow - UPDATE multiple columns

Start UPDATE statement

↓

Specify table to update

↓

Set new values for multiple columns

↓

Apply WHERE condition to select rows

↓

Execute update on selected rows

↓

Finish and return number of rows updated

The UPDATE statement changes values in multiple columns for rows that meet the WHERE condition.

Execution Sample

SQL

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

This query increases salary by 10% and changes department to 'Sales' for employees in 'Marketing'.

Execution Table

Step	Action	Row ID	Old salary	Old department	New salary	New department	Condition Met	Result
1	Check row	101	50000	Marketing	55000	Sales	Yes	Update applied
2	Check row	102	60000	Sales	60000	Sales	No	No update
3	Check row	103	55000	Marketing	60500	Sales	Yes	Update applied
4	Check row	104	70000	HR	70000	HR	No	No update
5	Finish	-	-	-	-	-	-	2 rows updated

💡 All rows checked; only rows with department 'Marketing' updated.

Variable Tracker

Variable	Start	After Row 101	After Row 102	After Row 103	After Row 104	Final
salary_101	50000	55000	55000	55000	55000	55000
department_101	Marketing	Sales	Sales	Sales	Sales	Sales
salary_102	60000	60000	60000	60000	60000	60000
department_102	Sales	Sales	Sales	Sales	Sales	Sales
salary_103	55000	55000	55000	60500	60500	60500
department_103	Marketing	Marketing	Marketing	Sales	Sales	Sales
salary_104	70000	70000	70000	70000	70000	70000
department_104	HR	HR	HR	HR	HR	HR

Key Moments - 2 Insights

Why are only some rows updated and not all?

Only rows where the WHERE condition is true (department = 'Marketing') are updated, as shown in execution_table rows 1 and 3.

Does the UPDATE change columns not listed in SET?

No, only columns specified in SET are changed. Other columns keep their original values, as seen in rows 2 and 4 where no update occurs.

Visual Quiz - 3 Questions

Look at the execution table, what is the new salary of row 103 after the update?

A 60500

B 55000

C 60000

D 70000

💡 Hint

Check the 'New salary' column for row 103 in the execution_table.

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

A Step 1

B Step 2

C Step 3

D Step 4

💡 Hint

Look at the 'Condition Met' column in execution_table for each step.

If the WHERE clause was removed, how would the execution table change?

A Only rows with salary > 60000 would update

B No rows would be updated

C All rows would be updated

D Only rows with department 'Sales' would update

💡 Hint

Without WHERE, UPDATE applies to all rows, so all would show 'Update applied' in the result.

Concept Snapshot

UPDATE multiple columns syntax:
UPDATE table_name
SET column1 = value1, column2 = value2
WHERE condition;
Only rows matching WHERE are updated.
Columns not listed remain unchanged.

Full Transcript

The UPDATE statement changes values in multiple columns for rows that meet the WHERE condition. In the example, employees in the Marketing department have their salary increased by 10% and their department changed to Sales. The execution table shows each row checked, whether it meets the condition, and if it is updated. Only rows 101 and 103 meet the condition and are updated. The variable tracker shows how salary and department values change step-by-step. Key moments clarify why only some rows update and that only specified columns change. The quiz tests understanding of the updated values, condition checks, and effects of removing the WHERE clause.

Practice

1. What does the SQL UPDATE statement do when you specify multiple columns in the SET clause?

easy

A. It deletes the rows that match the condition.

B. It only updates the first column listed and ignores the rest.

C. It creates new rows with the specified column values.

D. It changes the values of all specified columns in the selected rows.

Solution

1. Step 1: Understand the UPDATE statement

   The UPDATE statement modifies existing rows in a table.

2. Step 2: Effect of multiple columns in SET clause

   When multiple columns are listed in SET, all those columns are updated in the rows that match the WHERE condition.

3. Final Answer:

   It changes the values of all specified columns in the selected rows. -> Option D

4. Quick Check:

   UPDATE with multiple columns updates all listed columns [OK]

Hint: SET updates all listed columns together [OK]

Common Mistakes:

• Thinking UPDATE adds new rows
• Believing UPDATE deletes rows
• Assuming only first column updates

2. Which of the following is the correct syntax to update two columns, price and stock, in a table named products?

easy

A. UPDATE products SET price = 10, stock = 50 WHERE id = 1;

B. UPDATE products (price = 10, stock = 50) WHERE id = 1;

C. UPDATE products SET (price, stock) = (10, 50) WHERE id = 1;

D. UPDATE products WHERE id = 1 SET price = 10, stock = 50;

Solution

1. Step 1: Recall correct UPDATE syntax

   The correct syntax is UPDATE table_name SET column1 = value1, column2 = value2 WHERE condition;

2. Step 2: Check each option

   UPDATE products SET price = 10, stock = 50 WHERE id = 1; matches the correct syntax exactly. The other options have syntax errors.

3. Final Answer:

   UPDATE products SET price = 10, stock = 50 WHERE id = 1; -> Option A

4. Quick Check:

   SET column = value pairs separated by commas [OK]

Hint: Use SET column=value, column=value syntax [OK]

Common Mistakes:

• Using parentheses incorrectly in SET clause
• Placing WHERE before SET
• Missing commas between column assignments

3. Given the table employees with columns salary and bonus, what will be the result of this query?

UPDATE employees SET salary = salary + 1000, bonus = 500 WHERE department = 'Sales';

medium

A. All employees get salary and bonus updated regardless of department.

B. Only the salary of Sales employees increases; bonus remains unchanged.

C. All employees in Sales get their salary increased by 1000 and bonus set to 500.

D. Syntax error because multiple columns cannot be updated together.

Solution

1. Step 1: Understand the WHERE clause effect

   The WHERE clause limits updates to rows where department = 'Sales'.

2. Step 2: Analyze SET clause changes

   Salary increases by 1000 and bonus is set to 500 for those rows only.

3. Final Answer:

   All employees in Sales get their salary increased by 1000 and bonus set to 500. -> Option C

4. Quick Check:

   WHERE filters rows; SET updates all listed columns [OK]

Hint: WHERE limits rows; SET updates all columns listed [OK]

Common Mistakes:

• Ignoring WHERE and updating all rows
• Thinking bonus stays unchanged
• Believing multiple columns update causes error

4. Identify the error in this SQL statement:

UPDATE orders SET status = 'Shipped' stock = 0 WHERE order_id = 123;

medium

A. WHERE clause should come before SET clause.

B. Missing comma between column assignments in SET clause.

C. Incorrect table name used.

D. Quotes around 'Shipped' should be double quotes.

Solution

1. Step 1: Check SET clause syntax

   Multiple columns must be separated by commas in SET clause.

2. Step 2: Identify missing comma

   Between status = 'Shipped' and stock = 0, a comma is missing.

3. Final Answer:

   Missing comma between column assignments in SET clause. -> Option B

4. Quick Check:

   Separate columns with commas in SET [OK]

Hint: Put commas between each column=value pair [OK]

Common Mistakes:

• Omitting commas between columns
• Placing WHERE before SET
• Using wrong quotes for strings

5. You want to update the price and discount columns in the products table only for items where category is 'Electronics' and current stock is less than 10. Which query correctly does this?

hard

A. UPDATE products SET price = price * 0.9, discount = 10 WHERE category = 'Electronics' AND stock < 10;

B. UPDATE products SET price = price * 0.9, discount = 10 WHERE category = 'Electronics' OR stock < 10;

C. UPDATE products SET price = price * 0.9 discount = 10 WHERE category = 'Electronics' AND stock < 10;

D. UPDATE products SET price = price * 0.9, discount = 10 WHERE category = 'Electronics' AND stock > 10;

Solution

1. Step 1: Understand the condition requirements

   We want to update only rows where category is 'Electronics' AND stock is less than 10.

2. Step 2: Check each option's WHERE clause and syntax

   UPDATE products SET price = price * 0.9, discount = 10 WHERE category = 'Electronics' AND stock < 10; uses AND with correct conditions and proper syntax. UPDATE products SET price = price * 0.9, discount = 10 WHERE category = 'Electronics' OR stock < 10; uses OR, which updates more rows. UPDATE products SET price = price * 0.9 discount = 10 WHERE category = 'Electronics' AND stock < 10; misses a comma between assignments. UPDATE products SET price = price * 0.9, discount = 10 WHERE category = 'Electronics' AND stock > 10; uses stock > 10, which is incorrect.

3. Final Answer:

   UPDATE products SET price = price * 0.9, discount = 10 WHERE category = 'Electronics' AND stock < 10; -> Option A

4. Quick Check:

   Use AND for combined conditions and commas between columns [OK]

Hint: Use AND for all conditions; separate columns with commas [OK]

Common Mistakes:

• Using OR instead of AND in WHERE
• Missing commas between columns
• Wrong comparison operators in WHERE