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。