Question

I want a query to return all rows and all columns with one caveat: if, in a given row, colN is null, then instead return the string ‘FOO’.

Why dont I just use SELECT col1, col2, ..., COALESCE(colN, 'FOO')?

I am implementing an abstract interface and thus I am required to use SELECT queries which SELECT * (because I cannot make assumptions on what columns there are). I can only assume 1 columns exists: colN.

What would this provide me?

I need this because this query is used in combination with a UNION and this allows me to keep track of the origin of the data.

Any ideas on how to do this?

Answer 1

One thing you could do is

SELECT *, COALESCE(colN, 'FOO') as CoalescedColN

if it’s possible to adjust the other select(s) in the UNION accordingly