La manière standard SQL de faire cela serait :
SELECT COALESCE(field1, '') || COALESCE(field2, '') || COALESCE(field3, '') FROM table1
Exemple :
INSERT INTO table1 VALUES ('hello', null, 'world');
SELECT COALESCE(field1, '') || COALESCE(field2, '') || COALESCE(field3, '') FROM table1;
helloworld
