今天有同事在问 复制表的时候 会把表的 not null 属性也复制过来，而他要求对复制过来的字段不加not null 字段

SQL> desc DW_ACCOUNT

名称                                      是否为空? 类型

----------------------------------------- -------- ----------------------------

ACCT_ID                                   NOT NULL NUMBER(12)

ACCT_CD                                            VARCHAR2(100)

AREA_ID                                            NUMBER(5)

AREA_NAME                                          VARCHAR2(200)

PARTY_ID                                           NUMBER(12)

ACCT_STATUS_CD                                     NUMBER(5)

ACCT_STATUS                                        VARCHAR2(200)

ACCT_STATUS_REASON_CD                              NUMBER(5)

CREDIT_CLASS_CD                                    NUMBER(5)

LIMIT_QTY                                          NUMBER(12)

PROD_ID                                            NUMBER(12)

ACCT_TYPE_CD                                       NUMBER(5)

START_DT                                           DATE

IF_FREE                                            VARCHAR2(1)

ACCT_NAME                                          VARCHAR2(200)

RELATED_ACCT_ID                                    NUMBER(12)

PAYMENT_ACCOUNT_ID                                 NUMBER(12)

这里可以看到 ACCT_ID 是 NOT NULL的限制，我们这里复制DW_ACCOUNT的表结构

SQL> create table zyp_test as select * from dw_account where 1=2;

表已创建。

SQL> desc zyp_test;

名称                                      是否为空? 类型

----------------------------------------- -------- ----------------------------

ACCT_ID                                   NOT NULL NUMBER(12)

ACCT_CD                                            VARCHAR2(100)

AREA_ID                                            NUMBER(5)

AREA_NAME                                          VARCHAR2(200)

PARTY_ID                                           NUMBER(12)

ACCT_STATUS_CD                                     NUMBER(5)

ACCT_STATUS                                        VARCHAR2(200)

ACCT_STATUS_REASON_CD                              NUMBER(5)

CREDIT_CLASS_CD                                    NUMBER(5)

LIMIT_QTY                                          NUMBER(12)

PROD_ID                                            NUMBER(12)

ACCT_TYPE_CD                                       NUMBER(5)

START_DT                                           DATE

IF_FREE                                            VARCHAR2(1)

ACCT_NAME                                          VARCHAR2(200)

RELATED_ACCT_ID                                    NUMBER(12)

PAYMENT_ACCOUNT_ID                                 NUMBER(12)

可以看到 NOT NULL的属性也随之被复制过来了，如果能够在复制的时候 不复制NOT NULL的属性呢？

SQL> drop table zyp_test;

表已删除。

SQL> purge table zyp_test;

表已清除。

SQL> create table zyp_test (acct_id null, acct_cd not null) as select acct_id,ac

ct_cd from dw_account where 1=2;

表已创建。

SQL> desc zyp_test;

名称                                      是否为空? 类型

----------------------------------------- -------- ----------------------------

ACCT_ID                                            NUMBER(12)

ACCT_CD                                   NOT NULL VARCHAR2(100)

由于字段太多我就不做完全的复制了，这里其实可以发现 我们可以将源表的字段属性进行更改，NULL和NOT NULL都可以进行设置，当然如果在字段后面不加NULL或者NOT NULL的话，复制的表就会完全继承源表的字段属性。

那么复制过来的原本非空(NOT NULL)的 会不会有值呢？

再次进行测试：

SQL> create table zyp_test (acct_id null, acct_cd not null) as select acct_id,ac

ct_cd from dw_account where rownum<2;

表已创建。

SQL> select * from zyp_test;

ACCT_ID   ACCT_CD

--------------------------------------------------------------------------------

8.2000E+11   822818663

由此可以看到，字段属性发生改变不会对非空字段修改为允许空 字段造成影响，而如果将允许空字段改为非空字段，遇到null值就会报错了。

SQL> CREATE TABLE zyp_test (acct_id null, credit_class_cd NOT NULL) AS SELECT ac

ct_id,credit_class_cd FROM DW_ACCOUNT WHERE ROWNUM<2;

CREATE TABLE zyp_test (acct_id null, credit_class_cd NOT NULL) AS SELECT acct_id

,credit_class_cd FROM DW_ACCOUNT WHERE ROWNUM<2

*

第 1 行出现错误:

ORA-01400: 无法将 NULL 插入 ("STATA"."ZYP_TEST"."CREDIT_CLASS_CD")