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

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 to get its value.

Edit: This would be SQL Server.

Answer

One approach for Oracle:

SELECT val
FROM myTable
UNION ALL
SELECT 'DEFAULT'
FROM dual
WHERE NOT EXISTS (SELECT * FROM myTable)

Or alternatively in Oracle:

SELECT NVL(MIN(val), 'DEFAULT')
FROM myTable

Or alternatively in SqlServer:

SELECT ISNULL(MIN(val), 'DEFAULT')
FROM myTable

These use the fact that MIN() returns NULL when there are no rows.