Oracle 의 empty string 과 NULL

트리거 를 사용 하여 ORA - 01400 을 피하 기 위해 Oracle Not Null 열 에 빈 문자열 을 삽입 하 는 방법 (문서 ID 1224216.1)
APPLIES TO:
Oracle Server - Enterprise Edition - Version: 9.2.0.8 and later   [Release: 9.2 and later ] Information in this document applies to any platform.
GOAL
Given a table where a character column is defined as not null:   create table tester (id number not null, dat varchar2(30) default ' ' not null);
Why does the default value not get used in the following statements?     insert into tester values (1, '');
insert into tester values (1, null);
ERROR at line 1: ORA-01400: cannot insert NULL into ("REFRESH"."TESTER"."DAT") How might you still insert a record in these circumstances?  
Note that the string value '' (no space) is seen by Oracle as a null per documentation: Oracle� Database SQL Language Reference 11g Release 2 (11.2) Part Number E17118-03 E021-02, CHARACTER VARYING data type (Oracle does not distinguish a zero-length VARCHAR string from NULL)
 
SOLUTION
The "DEFAULT" column option does not work in this scenario because a value, albeit null, was provided in the insert for the dat column.  The default value is only used if the column is omitted from the insert statement. To utilize the default value defined at the column-level, the insert would need to be written as either:   insert into tester (id)  values (1);
insert into tester values (1, default);
In the case where a value is supplied but seen as null by Oracle, then use a trigger to provide a valid value:   create or replace trigger tester_null_ck_trig
before insert or update of dat on tester
for each row
declare
begin
if :new.dat is null then
:new.dat := ' ';
end if;
end;
/

insert into tester values (1, '');
insert into tester values (1, null);
 
REFERENCES
http://download.oracle.com/docs/cd/E11882_01/server.112/e17118/ap_standard_sql003.htm#g14847
댓 글 자 주석:
다음은 Oracle 10g 문서 에서 이 점 에 대한 설명 입 니 다.
Oracle 의 핵심 SQL: 2003 에 대한 준수 성
https://docs.oracle.com/cd/B19306_01/server.102/b14200/ap_standard_sql003.htm