Returns the first non-NULL expression from a list. This function is identical to the ISNULL function.
COALESCE( expression, expression [ , ...] )
expression Any expression.
At least two expressions must be passed into the function, and all expressions must be comparable.
The result is NULL only if all the arguments are NULL.
The parameters can be of any scalar type, but not necessarily same type.
For a more detailed description of how the database server processes this function, see ISNULL function [Miscellaneous].
SQL/2003 Core feature.
The following statement returns the value 34.
SELECT COALESCE( NULL, 34, 13, 0 );