RIGHT JOIN in MySQL - Step-by-Step Execution

Concept Flow - RIGHT JOIN

Start with LEFT table

↓

Match rows in RIGHT table

↓

Include all rows from RIGHT table

↓

If no match, LEFT columns NULL

↓

Combine rows into result

↓

Output final joined table

RIGHT JOIN returns all rows from the right table and matched rows from the left table. If no match, left side is NULL.

Execution Sample

MySQL

SELECT A.id, A.name, B.city
FROM A RIGHT JOIN B ON A.id = B.a_id;

This query returns all rows from table B and matching rows from table A based on id and a_id.

Execution Table

Step	Action	Left Table Row	Right Table Row	Match Condition	Result Row
1	Check B row with a_id=1	A.id=1, name='Ann'	B.a_id=1, city='NY'	1=1 (True)	id=1, name='Ann', city='NY'
2	Check B row with a_id=2	A.id=2, name='Bob'	B.a_id=2, city='LA'	2=2 (True)	id=2, name='Bob', city='LA'
3	Check B row with a_id=4	No matching A row	B.a_id=4, city='SF'	NULL=4 (False)	id=NULL, name=NULL, city='SF'
4	No more B rows	N/A	N/A	N/A	END

💡 All rows from right table B processed; unmatched left rows set to NULL.

Variable Tracker

Variable	Start	After 1	After 2	After 3	Final
Current B row	None	a_id=1, city='NY'	a_id=2, city='LA'	a_id=4, city='SF'	None
Current A row	None	id=1, name='Ann'	id=2, name='Bob'	No match (NULL)	None
Result row	None	id=1, name='Ann', city='NY'	id=2, name='Bob', city='LA'	id=NULL, name=NULL, city='SF'	None

Key Moments - 2 Insights

Why do some columns from the left table show NULL in the result?

Because RIGHT JOIN includes all rows from the right table even if there is no matching row in the left table, so left table columns are NULL for unmatched rows (see execution_table row 3).

Does RIGHT JOIN include all rows from the left table?

No, RIGHT JOIN includes all rows from the right table only. Left table rows appear only if they match (see execution_table rows 1 and 2).

Visual Quiz - 3 Questions

Look at the execution table, what is the result row at step 3?

A id=4, name='Dan', city='SF'

B id=NULL, name=NULL, city='SF'

C id=3, name='Cara', city=NULL

D No result row

💡 Hint

Check execution_table row 3 under 'Result Row' column.

At which step does the join find no matching left table row?

A Step 1

B Step 2

C Step 3

D Step 4

💡 Hint

Look for 'No matching A row' in execution_table under 'Left Table Row'.

If we changed RIGHT JOIN to LEFT JOIN, which table's rows would all appear?

A All rows from table A (left table)

B All rows from table B (right table)

C Only matching rows from both tables

D No rows at all

💡 Hint

RIGHT JOIN includes all right table rows; LEFT JOIN includes all left table rows.

Concept Snapshot

RIGHT JOIN syntax:
SELECT columns
FROM left_table RIGHT JOIN right_table
ON join_condition;

Returns all rows from right_table,
matching rows from left_table,
NULLs if no match on left side.

Full Transcript

RIGHT JOIN in SQL returns all rows from the right table and matching rows from the left table. If a row in the right table has no matching row in the left table, the left table columns are filled with NULL. The execution flow starts by scanning each row in the right table, then tries to find matching rows in the left table based on the join condition. Matched rows are combined into the result. Unmatched right table rows still appear with NULLs for left table columns. This is different from LEFT JOIN, which returns all rows from the left table instead. The example query selects id and name from table A and city from table B, joining on A.id = B.a_id. The execution table shows step-by-step how each row from B is matched or not matched with A, and how the result rows are formed.