COALESCE
Evaluates the arguments in order and returns the current value of the first expression that initially does not evaluate to NULL.
Syntax
COALESCE ( expression [ ,...n ] )
Arguments
expression
Is an expression of any type.
Return types
Returns the data type of expression with the highest data type precedence. If all expressions are nonnullable, the result is typed as nonnullable.
Examples
SELECT COALESCE(NULL, NULL, NULL, 1, 2, 3);