WHERE with IN list in SQL - Step-by-Step Execution

Concept Flow - WHERE with IN list

Start Query

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Evaluate WHERE clause

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Check if column value IN list?

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Include row

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Return Result Rows

The query checks each row's column value against a list. If the value is in the list, the row is included in the result.

Execution Sample

SQL

SELECT * FROM employees
WHERE department IN ('Sales', 'HR', 'IT');

This query selects all employees who work in Sales, HR, or IT departments.

Execution Table

Step	Row ID	department value	Condition: department IN ('Sales','HR','IT')	Include Row?
1	101	Sales	Sales IN list → True	Yes
2	102	Marketing	Marketing IN list → False	No
3	103	HR	HR IN list → True	Yes
4	104	Finance	Finance IN list → False	No
5	105	IT	IT IN list → True	Yes
6	106	Support	Support IN list → False	No
7	N/A	N/A	No more rows	Stop

💡 All rows checked; query returns rows where department is in the given list.

Variable Tracker

Variable	Start	After Row 1	After Row 2	After Row 3	After Row 4	After Row 5	After Row 6	Final
Current Row ID	N/A	101	102	103	104	105	106	End
Current department	N/A	Sales	Marketing	HR	Finance	IT	Support	End
Include Row?	N/A	Yes	No	Yes	No	Yes	No	End

Key Moments - 2 Insights

Why does the query exclude rows where the department is not in the list?

Because the WHERE clause condition 'department IN (...)' evaluates to False for those rows, so they are filtered out as shown in execution_table rows 2, 4, and 6.

What happens if the department value is NULL?

NULL values do not match any value in the IN list, so the condition evaluates to Unknown (treated as False), and those rows are excluded.

Visual Quiz - 3 Questions

Look at the execution_table, what is the 'Include Row?' value for Row ID 103?

A No

B Unknown

C Yes

D Not checked

💡 Hint

Check the row with Row ID 103 in the execution_table under 'Include Row?' column.

At which step does the condition 'department IN list' become False for the first time?

A Step 2

B Step 3

C Step 1

D Step 4

💡 Hint

Look at the 'Condition' column in execution_table and find the first 'False' value.

If we add 'Support' to the IN list, how would the 'Include Row?' value change for Row ID 106?

A Remain No

B Change from No to Yes

C Change to Unknown

D Row would be excluded anyway

💡 Hint

Refer to variable_tracker and execution_table rows for Row ID 106 and consider the IN list membership.

Concept Snapshot

WHERE with IN list:
Use WHERE column IN (value1, value2, ...)
Filters rows where column matches any listed value.
Rows not matching are excluded.
NULL values do not match any list item.
Useful for checking multiple possible values easily.

Full Transcript

This visual execution shows how the SQL WHERE clause with IN list works. The query checks each row's department value against a list of departments: 'Sales', 'HR', and 'IT'. For each row, if the department is in the list, the row is included in the result. Otherwise, it is excluded. The execution table traces each row's evaluation step by step. The variable tracker shows how the current row and decision change as the query processes rows. Key moments clarify why rows are excluded and how NULL values behave. The quiz tests understanding by asking about specific steps and effects of changing the IN list.