MarkLogic 10 Product Documentation
sql:ifnull

sql:ifnull(
   $expr1 as item()*,
   $expr2 as item()*
) as item()*

If the first expression is NULL, then the value of the second expression is returned. If not null, the first expression is returned.

Parameters
expr1	First expression to be evaluated.
expr2	Second expression to be evaluated.

sql:ifnull((),1) 
=>
1

MarkLogic 10 Product Documentationsql:ifnull