Question

我是SQL和Oracle的新手，所以为了练习，我创建了一个虚拟表来跟踪我的打字学习会话（因为我从未学会打字，所以我现在正在为它补偿），并设置了一个序列在Oracle中使用此查询：

CREATE SEQUENCE seq_keyboard_learning
MINVALUE 1
START WITH 1
INCREMENT BY 1
CACHE 10

我的意图是我的id列增加，但每次添加新值时它会从1跳到5等。为了完整起见，以下是我在设置此表时使用的一些查询。

CREATE TABLE keyboard_learning
(
emplid NUMBER CONSTRAINT emplid_pk PRIMARY KEY
,WPM NUMBER
,date_completed DATE
)

CREATE SEQUENCE seq_keyboard_learning
MINVALUE 1
START WITH 1
INCREMENT BY 1
CACHE 10

INSERT INTO keyboard_learning (emplid,wpm,date_completed)
VALUES (seq_keyboard_learning.nextval,15,'12-JUN-2012')

UPDATE keyboard_learning 
SET emplid = 1
WHERE emplid = 4

ALTER TABLE keyboard_learning
ADD attempt VARCHAR2(45)

INSERT INTO keyboard_learning
VALUES (seq_keyboard_learning.nextval,26,'6-JUN-2012','ASDFJKL:',2)

而不是每增加4个术语，我该如何调整？感谢

Answer 1

确保你没有无间隙序列基本上是不可能的。请记住，序列中的get是一个原子操作，因此如果您要插入记录并遇到错误，序列仍会递增。见下面的例子。

拥有缓存也会导致“丢失”序列。如果我在缓存中指定值10，则数据库将从序列中缓存10。如果只插入2行并关闭数据库，则丢弃其他8行。注：由Alex Poole编辑修正。

我希望这有助于理解序列的一些行为。

create table test
(id     number,
my_date date);

select seq.currval from dual;

insert into test
(id, my_date)
values (seq.nextval, 'foo'); -- will throw an exception

select seq.currval from dual;

结果是：

table TEST created. 
CURRVAL
-------
      1 


Error starting at line 31 in command: insert into test (id, my_date) values (seq.nextval, 'foo') Error report: SQL Error: ORA-01858: a non-numeric character was found where a numeric was expected
01858. 00000 -  "a non-numeric character was found where a numeric was expected"
*Cause:    The input data to be converted using a date format model was
           incorrect.  The input data did not contain a number where a number was
           required by the format model.
*Action:   Fix the input data or the date format model to make sure the
           elements match in number and type.  Then retry the operation. 
CURRVAL
-------
      2

序列递增每4个id而不是每1个像我设置的那样。神谕

1 个答案: