What value will be returned if one of the string expressions contains a NULL value in the CONCAT function?
What value will be returned depends a setting which syntax is
SET CONCAT NULL RETURN { NULL | STRING }
This option is used for string concatenation with null for the CONCAT built-in function or concatenate operator (||).
The default setting for this option is NULL. If this option is set to NULL, then any string concatenated with a null value will return null.
If the option is set to STRING, then any string concatenated with a null value will return the string, because the null value will be treated as an empty string.
For example:
dmSQL> select concat ('aaa', null);
CONCAT ('AAA', NULL)
===================================================================
NULL
1 rows selected
dmSQL> set concat null return string;
dmSQL> select concat ('aaa', null);
CONCAT ('AAA', NULL)
===================================================================
aaa
1 rows selected