C:\Users\123>sqlplus scott/system

SQL*Plus: Release 11.2.0.1.0 Production on Tue Jan 22 16:53:44 2013

Connected to:
Oracle Database 11g Enterprise Edition Release 11.2.0.1.0 - 64bit Production
With the Partitioning, OLAP, Data Mining and Real Application Testing options

SQL> create table t_substr(a varchar2(10));

Table created.

SQL> insert into t_substr values(null);

1 row created.

SQL> insert into t_substr values('zxy');

1 row created.

SQL> commit;

Commit complete.

SQL> select * from t_substr;

A
--------------------

zxy

SQL> select substr(a,1,2) from t_substr;

SUBSTR(A,1,2)
----------------

zx

SQL> select substr(null,1,2) from dual;

S
-
SQL> select substr(null,1,2) from t_substr;

S
-

小結:

1,如變數值為null,substr執行不會報錯,可以正常處理

null與substr

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