关于trigger过滤最大值的问题(54天)
关于trigger过滤最大值的问题(54天)
今天碰到一个问题，开发有一个比较紧的需要，想问问我数据库这边能不能帮上忙。
如果开发那边来做，需要改代码，如果数据库这边能临时支持，代码就可以多做些测试，然后再打补丁了。
需求的情况大体是这样:有一个表的字段是number(11,4),意味着数据保持4为精度，总共长度支持11位，最大值位9999999.9999
如果超过了那个最大值（比如99999999，有8个9），想在update语句update之前能够把那个值改成9999999就可以了。
听起来好像可以使用trigger来做。简单做了个测试。
新建一个表，字段last_threshold的数据类型为number(11,4)
SQL> create table test_number(last_threshold number(11,4),content varchar2(100));
Table created.
然后插入一些数据，可以看到，我插入的小数点后是5个9，也可以插入。
SQL> insert into test_number values(1.99999,'');
1 row created.
SQL> insert into test_number values(9999999.9999,'a');
1 row created.
SQL> insert into test_number values(9999999.9998,'b');
1 row created.
SQL> insert into test_number values(9.999999,'c');
1 row created.
SQL> commit;
Commit complete.
查看插入的数据情况，看到现实是下面的样子，有些疑惑，全都自作主张做了4舍5入了。
select *from test_number;
LAST_THRESHOLD CONTENT
-------------- ------------------------------
2
10000000 a
10000000 b
10 c
设置一下精度
SQL> col last_threshold format 99999999.99999
SQL> /
LAST_THRESHOLD CONTENT
--------------- ------------------------------
2.00000
9999999.99990 a
9999999.99980 b
10.00000 c
SQL> col last_threshold format 9999999.9999
SQL> /
LAST_THRESHOLD CONTENT
-------------- ------------------------------
2.0000
9999999.9999 a
9999999.9998 b
10.0000 c
想直接创建一个语句级的trigger，可惜失败了。
SQL> CREATE TRIGGER maxvalue_test
before UPDATE of LAST_THRESHOLD
ON test_number
begin
dbms_output.put_line(:old.last_threshold);
dbms_output.put_line(:new.last_threshold);
end;
/ 2 3 4 5 6 7 8
CREATE TRIGGER maxvalue_test
*
ERROR at line 1:
ORA-04082: NEW or OLD references not allowed in table level triggers
重头再来，先写一个trigger来测试一下是不是好使。
SQL> CREATE TRIGGER maxvalue_test
before UPDATE of LAST_THRESHOLD
ON test_number for each row
begin
dbms_output.put_line(:old.last_threshold);
dbms_output.put_line(:new.last_threshold);
end;
/ 2 3 4 5 6 7 8
Trigger created.
SQL> update test_number set last_threshold=9293.9999 where content='c';
10
9293.9999
1 row updated.
SQL> rollback;
Rollback complete.
SQL> select *from test_number;
LAST_THRESHOLD CONTENT
-------------- ------------------------------
2.0000
9999999.9999 a
9999999.9998 b
10.0000 c
可以看到行级的触发器做了多少的处理。 验证了3条记录。
SQL> update test_number set last_threshold=9999 where content is not null;
9999999.9999
9999
9999999.9998
9999
10
9999
3 rows updated.
SQL> commit;
Commit complete.
SQL> select *from test_number;
LAST_THRESHOLD CONTENT
-------------- ------------------------------
2.0000
9999.0000 a
9999.0000 b
9999.0000 c
尝试改成最大值
SQL> update test_number set last_threshold=9999999.9999 where content is null;
2
9999999.9999
1 row updated.
SQL> commit;
Commit complete.
SQL> select *from test_number;
LAST_THRESHOLD CONTENT
-------------- ------------------------------
9999999.9999
9999.0000 a
9999.0000 b
9999.0000 c
然后开始正式的测试。
drop trigger maxvalue_test;
CREATE TRIGGER maxvalue_test
before UPDATE of LAST_THRESHOLD
ON test_number for each row
begin
dbms_output.put_line('old: '||:old.last_threshold);
dbms_output.put_line('new: '||:new.last_threshold);
if (:new.last_threshold>9999999)
then
:new.last_threshold:=9999999;
dbms_output.put_line('change to: '||:new.last_threshold);
end if;
end;
/
但是测试的时候发现还是不行。
SQL> update test_number set last_threshold=99999999.9999 where content is null;
update test_number set last_threshold=99999999.9999 where content is null
*
ERROR at line 1:
ORA-01438: value larger than specified precision allowed for this column
drop trigger maxvalue_test;
那改成合理范围的值呢。比如改成100.
CREATE TRIGGER maxvalue_test
before UPDATE of LAST_THRESHOLD
ON test_number for each row
begin
dbms_output.put_line('old: '||:old.last_threshold);
dbms_output.put_line('new: '||:new.last_threshold);
if (:new.last_threshold<9999999)
then
:new.last_threshold:=100;
dbms_output.put_line('change to: '||:new.last_threshold);
end if;
end;
/
SQL> update test_number set last_threshold=999999.9 where content is null;
old: 999999.9999
new: 999999.9
change to: 100
1 row updated.
SQL> commit;
Commit complete.
SQL> select *from test_number;
LAST_THRESHOLD CONTENT
-------------- ------------------------------
100.0000
9999.0000 a
9999.0000 b
9999.0000 c
可以看到trigger的数据校验一定是在数据类型在合理范围之内。不过反过来一想也是合情合理。
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