ASSUME_NOT_NULL
Results in an equivalent non-Nullable value for a Nullable type. In case the original value is NULL the result is undetermined. 
Syntax
ASSUME_NOT_NULL(x);
Arguments
| Arguments | Description | 
|---|---|
| x | The original value. | 
Return Type
Returns the original datatype from the non-Nullable type; Returns the embedded non-Nullable datatype for Nullable type.
Examples
CREATE TABLE default.t_null ( x int,  y int null);
INSERT INTO default.t_null values (1, null), (2, 3);
SELECT ASSUME_NOT_NULL(y) FROM t_null;
+--------------------+
| ASSUME_NOT_NULL(y) |
+--------------------+
|                  0 |
|                  3 |
+--------------------+