oracle - ORACLE 12.2.01 从具有相似名称的不同表中选择列 --> 使用内部列标识符

Question

我编写了一个执行 UNION 的 SELECT，并在每个 UNION 部分中使用了一些 JOIN。连接的表具有部分相同的列标识符。如果执行“SELECT *”，ORACLE 决定显示内部列名而不是“真实”列名。

为了显示效果，我创建了两个表（列标识符部分相似，“TID”和“TNAME”）并用一些数据填充它们：

create table table_one (tid number(10), tname varchar2(10), t2id number(10));
create table table_two (tid number(10), tname varchar2(10));

insert into table_two values (1,'one');
insert into table_two values (2,'two');
insert into table_two values (3,'three');

insert into table_one values (1,'eins',1);
insert into table_one values (2,'zwei',2);
insert into table_one values (3,'drei',3);

之后我使用以下语句选择了列：

select * 
from table_one 
inner join table_two on table_two.tid = table_one.t2id
where table_one.tid = 1
union
select * 
from table_one 
inner join table_two on table_two.tid = table_one.t2id
where table_one.tid = 2;

并得到了这个令人困惑的结果：

QCSJ_C000000000300000 QCSJ_C000000000300002       T2ID QCSJ_C000000000300001 QCSJ_C000000000300004
                    1 eins                           1                     1 one
                    2 zwei                           2                     2 two

当使用表名编写语句以指定列时，一切都按我的预期工作：

select table_one.* , table_two.*
from table_one 
inner join table_two on table_two.tid = table_one.t2id
where table_one.tid = 1
minus
select * 
from table_one 
inner join table_two on table_two.tid = table_one.t2id
where table_one.tid = 2;

   TID TNAME            T2ID        TID TNAME
     1 eins                1          1 one
     2 zwei                2          2 two

有人能解释一下吗？

我用另外两个表扩展了我的测试，以防止在语句中重复使用表：

create table table_3 (tid number(10), tname varchar2(10), t4id number(10));
create table table_4 (tid number(10), tname varchar2(10));

insert into table_4 values (1,'one');
insert into table_4 values (2,'two');
insert into table_4 values (3,'three');

insert into table_3 values (1,'eins',1);
insert into table_3 values (2,'zwei',2);
insert into table_3 values (3,'drei',3);

select * 
from table_one 
inner join table_two on table_two.tid = table_one.t2id
where table_one.tid = 1
union
select * 
from table_3
inner join table_4 on table_4.tid = table_3.t4id
where table_3.tid = 2;

select * 
from table_one 
inner join table_two on table_two.tid = table_one.t2id
where table_one.tid = 1
union
select * 
from table_3
inner join table_4 on table_4.tid = table_3.t4id
where table_3.tid = 2;

结果是一样的。Oracle 使用内部标识符。

标签： oracleselectidentifier

Answer 1

根据 Oracle (DocId 2658003.1)，当满足三个条件时会发生这种情况：

1. ANSI 连接
2. 联合/联合所有
3. 同一个表在查询中出现多次

显然，当 Oracle 转换 ANSI 样式连接时，内部使用了“QCSJ_C”。

编辑：

找到一个最小的例子：

SELECT * FROM dual d1 JOIN dual d2 ON d1.dummy=d2.dummy
UNION
SELECT * FROM dual d1 JOIN dual d2 ON d1.dummy=d2.dummy;

QCSJ_C000000000300000 QCSJ_C000000000300001
X                     X

它可以通过使用非 ANSI 连接语法来修复：

SELECT * FROM dual d1, dual d2 WHERE d1.dummy=d2.dummy
UNION
SELECT * FROM dual d1, dual d2 WHERE d1.dummy=d2.dummy;

DUMMY DUMMY_1
X     X

或者，最好使用列名而不是*：

SELECT d1.dummy, d2.dummy FROM dual d1 JOIN dual d2 ON d1.dummy=d2.dummy
UNION
SELECT d1.dummy, d2.dummy FROM dual d1 JOIN dual d2 ON d1.dummy=d2.dummy;

DUMMY DUMMY_1
X     X