FULL OUTER JOIN behavior in SQL - Cheat Sheet & Quick Revision

Recall & Review

beginner

What does a FULL OUTER JOIN do in SQL?

It returns all rows from both tables, matching rows where possible. If there is no match, it fills with NULLs for the missing side.

beginner

How does FULL OUTER JOIN differ from INNER JOIN?

INNER JOIN returns only rows with matching keys in both tables. FULL OUTER JOIN returns all rows from both tables, matching where possible and filling NULLs where no match exists.

beginner

In a FULL OUTER JOIN, what happens if a row in the left table has no matching row in the right table?

The row from the left table appears in the result with NULL values for the right table's columns.

beginner

Write a simple SQL query using FULL OUTER JOIN between tables A and B on column id.

SELECT * FROM A FULL OUTER JOIN B ON A.id = B.id;

intermediate

Why might you use FULL OUTER JOIN instead of LEFT or RIGHT JOIN?

To get a complete view of all data from both tables, including unmatched rows from both sides.

What does FULL OUTER JOIN return?

A All rows from the left table only

B Only matching rows from both tables

C All rows from the right table only

D All rows from both tables, matching where possible, NULLs otherwise

FULL OUTER JOIN returns all rows from both tables, matching rows where possible and filling NULLs where no match exists.

If a row in the right table has no match in the left table, what does FULL OUTER JOIN do?

A Excludes the row

B Includes the row with NULLs for left table columns

C Includes the row with NULLs for right table columns

D Returns an error

FULL OUTER JOIN includes unmatched rows from both tables, filling NULLs for the missing side's columns.

Which JOIN type returns only rows with matching keys in both tables?

A FULL OUTER JOIN

B LEFT JOIN

C INNER JOIN

D RIGHT JOIN

INNER JOIN returns only rows where keys match in both tables.

What keyword is used in SQL for a FULL OUTER JOIN?

A FULL OUTER JOIN

B ALL JOIN

C OUTER JOIN

D FULL JOIN

The correct syntax is FULL OUTER JOIN to include all rows from both tables.

Which scenario best fits using FULL OUTER JOIN?

A You want all records from both tables, including unmatched

B You want all records from left table only

C You want only matching records

D You want only unmatched records

FULL OUTER JOIN returns all records from both tables, including unmatched rows.

Explain in your own words how FULL OUTER JOIN works and when you would use it.

Think about combining two lists fully, including unmatched items.

Write a simple SQL query using FULL OUTER JOIN and describe what the output will look like.

Use SELECT * FROM table1 FULL OUTER JOIN table2 ON condition.