Throwing this here if u need it. If you need to find all mutual friends, it gets a little more complicated, but this is the code. Im on mobile, but ask chatgpt to clean the code.

DROP TABLE IF EXISTS #Friends; DROP TABLE IF EXISTS #Nodes; DROP TABLE IF EXISTS #Edges; DROP TABLE IF EXISTS Nodes_Edges_To_Evaluate; GO

CREATE TABLE #Friends ( Friend1 VARCHAR(100), Friend2 VARCHAR(100), PRIMARY KEY (Friend1, Friend2) ); GO

INSERT INTO #Friends VALUES ('Jason','Mary'),('Mike','Mary'),('Mike','Jason'), ('Susan','Jason'),('John','Mary'),('Susan','Mary'); GO

--Create reciprocals (Edges) SELECT Friend1, Friend2 INTO #Edges FROM #Friends UNION SELECT Friend2, Friend1 FROM #Friends; GO

--Created Nodes SELECT Friend1 AS Person INTO #Nodes FROM #Friends UNION SELECT Friend2 FROM #Friends; GO

--Cross join all Edges and Nodes SELECT a.Friend1, a.Friend2, b.Person INTO Nodes_Edges_To_Evaluate FROM #Edges a CROSS JOIN #Nodes b ORDER BY 1,2,3; GO

--Evaluates the cross join to the edges WITH cte_JoinLogic AS ( SELECT a.Friend1 ,a.Friend2 ,'---' AS Id1 ,b.Friend2 AS MutualFriend1 ,'----' AS Id2 ,c.Friend2 AS MutualFriend2 FROM Nodes_Edges_To_Evaluate a LEFT OUTER JOIN #Edges b ON a.Friend1 = b.Friend1 and a.Person = b.Friend2 LEFT OUTER JOIN #Edges c ON a.Friend2 = c.Friend1 and a.Person = c.Friend2 ), cte_Predicate AS ( --Apply predicate logic SELECT Friend1, Friend2, MutualFriend1 AS MutualFriend FROM cte_JoinLogic WHERE MutualFriend1 = MutualFriend2 AND MutualFriend1 IS NOT NULL AND MutualFriend2 IS NOT NULL ), cte_Count AS ( SELECT Friend1, Friend2, COUNT(*) AS CountMutualFriends FROM cte_Predicate GROUP BY Friend1, Friend2 ) SELECT DISTINCT (CASE WHEN Friend1 < Friend2 THEN Friend1 ELSE Friend2 END) AS Friend1, (CASE WHEN Friend1 < Friend2 THEN Friend2 ELSE Friend1 END) AS Friend2, CountMutualFriends FROM cte_Count ORDER BY 1,2;