[20180904]工作中一个错误.txt

[20180904]工作中一个错误.txt

--//昨天看我提交一份修改建议,发现自己写的sql语句存在错误.
--//链接:http://blog.itpub.net/267265/viewspace-2213259/
--//里面提到:
5f2atm993xz6w
update pd_pmxs set pdbz =:"sys_b_0" , status =:"sys_b_1" where rdid =:1
修改为
update pd_pmxs set pdbz =:"sys_b_0" , status =:"sys_b_1" where rdid =:1 and  pdbz <> :"sys_b_0" and status <>:"sys_b_1"

--//这样修改是有问题,通过一个例子说明:

1.环境:
scott@test01p> @ ver1

port_string                    version        banner                                                                               con_id
------------------------------ -------------- -------------------------------------------------------------------------------- ----------
ibmpc/win_nt64-9.1.0           12.1.0.1.0     oracle database 12c enterprise edition release 12.1.0.1.0 - 64bit production              0

scott@test01p> create table t (id number,a number,b number);
table created.

insert into t values (1,0,0);
insert into t values (1,0,1);
insert into t values (1,1,0);
insert into t values (1,1,1);
insert into t values (1,2,2);
insert into t values (1,2,1);

commit;

2.测试:
scott@test01p> select * from t where id=1 and a<>1 and b<>1;
        id          a          b
---------- ---------- ----------
         1          0          0
         1          2          2

--//可以发现这样写仅仅显示两条.如果按照前面的语句执行dml,就存在错误了.

update pd_pmxs set pdbz =1 , status =1 where rdid =:1
--//修改为
update pd_pmxs set pdbz =1 , status =1 where rdid =:1 and pdbz <>1 and status <>1

--//这样仅仅(pdbz, status) =(0,0),(2,2) 才会修改.其它情况不会修改,实际上这是一个集合问题.
--//执行如下就对了.

scott@test01p> select * from t where id=1 and (a<>1 or b<>1);
        id          a          b
---------- ---------- ----------
         1          0          0
         1          0          1
         1          1          0
         1          2          2
         1          2          1

--//也就是我上面的语句要修改如下:
update pd_pmxs set pdbz =:"sys_b_0" , status =:"sys_b_1" where rdid =:1 and  (pdbz <> :"sys_b_0" or status <>:"sys_b_1" );

--//实际上面的写法很容易混乱,写成集合的形式就容易理解也不会错误.

scott@test01p> select * from t where id=1 and (a,b) not in (1,1);
select * from t where id=1 and (a,b) not in (1,1)
                                            *
error at line 1:
ora-00920: invalid relational operator
--//集合还要加一个括号.

scott@test01p> select * from t where id=1 and (a,b) not in ((1,1));
        id          a          b
---------- ---------- ----------
         1          0          0
         1          0          1
         1          1          0
         1          2          2
         1          2          1


--//这样上面的修改如下:
5f2atm993xz6w
update pd_pmxs set pdbz =:"sys_b_0" , status =:"sys_b_1" where rdid =:1
修改为
update pd_pmxs set pdbz =:"sys_b_0" , status =:"sys_b_1" where rdid =:1 and  (pdbz,status) not in(( :"sys_b_0" , :"sys_b_1" );

--//这样也好理解也不会错误,给自己一个工作中提一个醒.