INNER JOIN with multiple conditions in SQL - Step-by-Step Execution

Concept Flow - INNER JOIN with multiple conditions

Start with Table A

↓

Start with Table B

↓

Check Condition 1: A.col1 = B.col1

Yes↓

Check Condition 2: A.col2 = B.col2

Yes↓

Combine rows from A and B

↓

Add combined row to result

↓

Repeat for all rows in A and B

↓

End with result set of matched rows

The INNER JOIN compares rows from two tables and includes only those where all specified conditions are true.

Execution Sample

SQL

SELECT *
FROM Employees E
INNER JOIN Departments D
ON E.DeptID = D.DeptID
AND E.Location = D.Location;

This query joins Employees and Departments where both DeptID and Location match.

Execution Table

Step	E.DeptID	E.Location	D.DeptID	D.Location	Condition 1 (E.DeptID = D.DeptID)	Condition 2 (E.Location = D.Location)	Row Included?
1	10	NY	10	NY	True	True	Yes
2	10	NY	10	LA	True	False	No
3	20	LA	20	LA	True	True	Yes
4	20	LA	30	LA	False	True	No
5	30	NY	30	NY	True	True	Yes
6	30	NY	10	NY	False	True	No
7	-	-	-	-	-	-	End of rows

💡 All rows compared; only rows where both conditions are true are included.

Variable Tracker

Variable	Start	After Step 1	After Step 2	After Step 3	After Step 4	After Step 5	After Step 6	Final
Row Included?	N/A	Yes	No	Yes	No	Yes	No	Final result includes rows 1, 3, and 5

Key Moments - 2 Insights

Why are some rows with matching DeptID excluded?

Rows are excluded if the second condition (Location match) is false, as shown in execution_table rows 2 and 6.

Does INNER JOIN include rows if only one condition matches?

No, both conditions must be true for a row to be included, as seen in rows 2 and 4 where one condition fails.

Visual Quiz - 3 Questions

Look at the execution table, at step 4, why is the row not included?

A Because Condition 2 is false

B Because both conditions are true

C Because Condition 1 is false

D Because both conditions are false

💡 Hint

Check the values under Condition 1 and Condition 2 columns at step 4 in the execution_table.

At which steps are rows included in the result?

A Steps 1, 3, 5

B Steps 2, 4, 6

C Steps 1, 2, 3

D Steps 4, 5, 6

💡 Hint

Look at the 'Row Included?' column in the execution_table for 'Yes' values.

If the second condition (Location match) was removed, what would happen to the included rows?

A No change in included rows

B More rows would be included

C Fewer rows would be included

D Query would return no rows

💡 Hint

Removing a condition relaxes the join criteria, so check how many rows satisfy only the first condition.

Concept Snapshot

INNER JOIN with multiple conditions syntax:
SELECT * FROM A INNER JOIN B ON A.col1 = B.col1 AND A.col2 = B.col2;
Only rows matching all conditions appear in the result.
Conditions are combined with AND.
Useful to filter joined rows precisely.

Full Transcript

This visual execution shows how an INNER JOIN with multiple conditions works. We start with two tables, Employees and Departments. For each pair of rows, we check if the DeptID matches and if the Location matches. Only when both conditions are true do we include the combined row in the result. The execution table lists each comparison step, showing which rows pass both conditions and are included. The variable tracker highlights how the inclusion decision changes step by step. Key moments clarify why some rows are excluded despite partial matches. The quiz tests understanding by asking about specific steps and the effect of conditions. This helps beginners see how multiple conditions in INNER JOIN filter the results carefully.