Question

当我更改标识列的属性时，已经填写的表的标识列的值会保留吗？

我有两个带有一个INTEGER标识列的表。在一个表table1中，我只想禁用此属性。在另一个表table2中，我想更改身份计数器的值范围。

执行此操作的想法如下：

db2 "alter table <table1> ALTER COLUMN <column> drop IDENTITY"

db2 "alter table <table2> ALTER COLUMN <column> drop IDENTITY" 
db2 "alter table <table2> ALTER COLUMN <column> set generated always as identity  
     (START WITH 1, INCREMENT BY 1, MINVALUE 1, MAXVALUE 65536, CYCLE, NO CACHE, NO ORDER)".

由于我仅更改表1中列的属性并增加表2中列的值范围，因此我希望保留受影响列中的值。还是将所有值始终都设置为空（带有删除IDENTITY）？

Answer 1

自己测试很容易，不是吗？

[db2inst1@somehost ~]$ db2 "create table test(f1 int not null generated always as identity, f2 varchar(20))"
DB20000I  The SQL command completed successfully.
[db2inst1@somehost ~]$ db2 "insert into test (f2) values ('foobar')"
DB20000I  The SQL command completed successfully.
[db2inst1@somehost ~]$ db2 "insert into test (f2) values ('foobar')"
DB20000I  The SQL command completed successfully.
[db2inst1@somehost ~]$ db2 "select * from test"

F1          F2
----------- --------------------
          1 foobar
          2 foobar

  2 record(s) selected.

[db2inst1@somehost ~]$ db2 "alter table test alter column f1 drop identity"
DB20000I  The SQL command completed successfully.
[db2inst1@somehost ~]$ db2 "select * from test"

F1          F2
----------- --------------------
          1 foobar
          2 foobar

  2 record(s) selected.

因此，不会，以前的IDENTITY的现有值将不会被修改。

但是请注意，如果您以table2的显示方式重新创建身份，它将至少生成一些与现有值重叠的值，从而导致重复的“身份”或插入异常。

[db2inst1@somehost ~]$ db2 "alter table test alter column f1 set generated always as identity
>      (START WITH 1, INCREMENT BY 1, MINVALUE 1)"
DB20000I  The SQL command completed successfully.
[db2inst1@somehost ~]$ db2 "insert into test (f2) values ('foobar')"
DB20000I  The SQL command completed successfully.
[db2inst1@somehost ~]$ db2 "select * from test"

F1          F2
----------- --------------------
          1 foobar
          2 foobar
          1 foobar

  3 record(s) selected.

当我更改DB2 v11数据库的Identity属性时，列内容会怎样？

1 个答案: