UPDATE with WHERE condition in SQL - Step-by-Step Execution

Concept Flow - UPDATE with WHERE condition

Start UPDATE statement

↓

Check WHERE condition for each row

↓

Update row

↓

End UPDATE

The UPDATE command checks each row against the WHERE condition. If true, it updates that row; if false, it skips it.

Execution Sample

SQL

UPDATE Employees
SET Salary = Salary + 500
WHERE Department = 'Sales';

This query increases the Salary by 500 for employees in the Sales department only.

Execution Table

Step	Row ID	Current Salary	Department	WHERE Condition (Department='Sales')	Action	New Salary
1	101	3000	Sales	True	Update	3500
2	102	3200	HR	False	Skip	3200
3	103	2800	Sales	True	Update	3300
4	104	4000	IT	False	Skip	4000
5	105	3100	Sales	True	Update	3600
6	-	-	-	-	End of rows	-

💡 All rows checked; only rows with Department='Sales' updated.

Variable Tracker

Row ID	Salary Before	Salary After
101	3000	3500
102	3200	3200
103	2800	3300
104	4000	4000
105	3100	3600

Key Moments - 2 Insights

Why are some rows not updated even though the UPDATE command runs?

Rows where the WHERE condition is False are skipped, as shown in execution_table rows 2 and 4.

What happens if the WHERE condition is missing?

Without WHERE, all rows would be updated. Here, only rows with Department='Sales' are updated.

Visual Quiz - 3 Questions

Look at the execution_table, what is the new salary of Row ID 103 after the update?

A 3500

B 2800

C 3300

D 3100

💡 Hint

Check the 'New Salary' column for Row ID 103 in the execution_table.

At which step does the WHERE condition evaluate to False?

A Step 2

B Step 3

C Step 1

D Step 5

💡 Hint

Look at the 'WHERE Condition' column in the execution_table for False values.

If the WHERE clause was removed, how would the 'Action' column change?

A All rows would be 'Skip'

B All rows would be 'Update'

C Only Sales rows would be 'Update'

D No rows would be updated

💡 Hint

Without WHERE, UPDATE affects every row as per SQL rules.

Concept Snapshot

UPDATE table_name
SET column = new_value
WHERE condition;

- Only rows matching WHERE condition are updated.
- Rows not matching are unchanged.
- Omitting WHERE updates all rows.

Full Transcript

The UPDATE statement changes data in a table. It checks each row against the WHERE condition. If the condition is true, it updates that row's data. If false, it leaves the row unchanged. For example, increasing salary only for employees in the Sales department updates only those rows. Rows in other departments remain the same. Without a WHERE clause, all rows would be updated. This visual shows step-by-step how each row is checked and updated or skipped.