UPDATE single column in SQL - Step-by-Step Execution

Concept Flow - UPDATE single column

Start

↓

Identify Table

↓

Set new value for one column

↓

Apply WHERE condition?

No→Update all rows

Yes↓

Update matching rows

↓

End

The UPDATE command changes values in one column of a table, optionally filtering rows with WHERE.

Execution Sample

SQL

UPDATE employees
SET salary = 60000
WHERE employee_id = 3;

This updates the salary of the employee with ID 3 to 60000.

Execution Table

Step	Action	Evaluation	Result
1	Identify table 'employees'	Table found	Ready to update
2	Set 'salary' = 60000	Prepare new value	Value ready
3	Check WHERE employee_id = 3	Row 1: employee_id=1 -> False	Skip row 1
4	Check WHERE employee_id = 3	Row 2: employee_id=2 -> False	Skip row 2
5	Check WHERE employee_id = 3	Row 3: employee_id=3 -> True	Update row 3 salary to 60000
6	Check WHERE employee_id = 3	Row 4: employee_id=4 -> False	Skip row 4
7	Finish update	All rows checked	Update complete

💡 All rows checked, only row with employee_id=3 updated

Variable Tracker

Variable	Start	After Step 3	After Step 5	Final
salary (row 1)	50000	50000	50000	50000
salary (row 2)	52000	52000	52000	52000
salary (row 3)	58000	58000	60000	60000
salary (row 4)	49000	49000	49000	49000

Key Moments - 2 Insights

Why does only one row get updated even though we set salary = 60000?

Because the WHERE condition filters rows. Only the row where employee_id = 3 matches and gets updated, as shown in execution_table rows 3 to 6.

What happens if we omit the WHERE clause?

Without WHERE, all rows get updated. The execution_table would skip the condition checks and update every row's salary.

Visual Quiz - 3 Questions

Look at the execution table, what is the salary of employee_id=3 after step 5?

A 58000

B 60000

C 52000

D 49000

💡 Hint

Check the 'Result' column at step 5 where the update happens.

At which step does the update command skip a row because the WHERE condition is false?

A Step 3

B Step 5

C Step 7

D Step 2

💡 Hint

Look at the evaluation for row 1 in the execution_table.

If the WHERE clause is removed, how would the execution_table change?

A Only the first row would be updated.

B No rows would be updated.

C All rows would be updated without condition checks.

D The update would fail with an error.

💡 Hint

Refer to the key moment about omitting WHERE clause.

Concept Snapshot

UPDATE table_name
SET column_name = new_value
[WHERE condition];

- Changes one column's value
- WHERE filters which rows update
- Without WHERE, all rows update

Full Transcript

The UPDATE single column command changes values in one column of a table. It starts by identifying the table, then prepares the new value. It checks each row against the WHERE condition. Only rows matching the condition get updated. Others stay the same. If no WHERE is given, all rows update. This example updates salary to 60000 for employee_id 3 only.