How to set a default row for a query that returns no rows?

Question

I need to know how to return a default row if no rows exist in a table. What would be the best way to do this? I\'m only returning a single column from this particular table

Answer 1

*SQL solution

Suppose you have a review table which has primary key "id".

SELECT * FROM review WHERE id = 1555
UNION ALL
SELECT * FROM review WHERE NOT EXISTS ( SELECT * FROM review where id = 1555 ) AND id = 1

if table doesn't have review with 1555 id then this query will provide a review of id 1.