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

Concept Flow - DELETE with WHERE condition

Start DELETE command

↓

Check WHERE condition on each row

↓

Mark row

↓

Delete marked rows

↓

End

The DELETE command checks each row against the WHERE condition. Rows that match are deleted; others stay.

Execution Sample

SQL

DELETE FROM Employees WHERE Department = 'Sales';

Deletes all rows from Employees table where Department is 'Sales'.

Execution Table

Step	Row ID	Department	WHERE Condition (Department='Sales')	Action
1	1	HR	False	Keep row
2	2	Sales	True	Mark for deletion
3	3	IT	False	Keep row
4	4	Sales	True	Mark for deletion
5	5	Marketing	False	Keep row
6	-	-	-	Delete rows marked for deletion (Row IDs 2,4)
7	-	-	-	End of DELETE command

💡 All rows checked; rows with Department='Sales' are deleted.

Variable Tracker

Variable	Start	After 1	After 2	After 3	After 4	After 5	Final
Rows in Employees	[1:HR,2:Sales,3:IT,4:Sales,5:Marketing]	[1:HR,2:Sales,3:IT,4:Sales,5:Marketing]	[1:HR,2:Sales,3:IT,4:Sales,5:Marketing]	[1:HR,2:Sales,3:IT,4:Sales,5:Marketing]	[1:HR,2:Sales,3:IT,4:Sales,5:Marketing]	[1:HR,2:Sales,3:IT,4:Sales,5:Marketing]	[1:HR,3:IT,5:Marketing]

Key Moments - 2 Insights

Why are only some rows deleted and not all?

Only rows where the WHERE condition is True are deleted, as shown in execution_table rows 2 and 4. Rows with False condition remain.

What happens if the WHERE condition is missing?

Without WHERE, all rows would be deleted. Here, the WHERE condition filters rows to delete only those matching 'Sales'.

Visual Quiz - 3 Questions

Look at the execution table, which row IDs are deleted?

A 1 and 3

B 2 and 4

C 3 and 5

D All rows

💡 Hint

Check the 'Action' column where rows are marked for deletion.

At which step does the DELETE command remove rows?

A Step 4

B Step 5

C Step 6

D Step 7

💡 Hint

Look for the step mentioning 'Delete rows marked for deletion'.

If the WHERE condition was Department = 'IT', which rows would be deleted?

A Row 3 only

B Rows 1 and 5

C Rows 2 and 4

D No rows

💡 Hint

Refer to the 'Department' values in the variable_tracker and execution_table.

Concept Snapshot

DELETE FROM table_name WHERE condition;
- Checks each row against condition.
- Deletes only rows where condition is true.
- Without WHERE, deletes all rows.
- Use carefully to avoid data loss.

Full Transcript

The DELETE command removes rows from a table that meet a specific condition given by WHERE. It checks each row one by one. If the condition is true, that row is deleted. If false, the row stays. For example, DELETE FROM Employees WHERE Department = 'Sales' deletes only employees in Sales. The execution table shows each row checked and action taken. Rows 2 and 4 match and are deleted. Rows 1, 3, and 5 do not match and remain. This selective deletion helps avoid removing all data accidentally. Always use WHERE to target specific rows.