请问这是ORACLE的Bug吗

[詩和遠方]

先准备数据：

CREATE TABLE Table_A(EID NUMBER PRIMARY KEY);
/
CREATE TABLE Table_B(EID NUMBER PRIMARY KEY,EMail VARCHAR2(300));
/

INSERT INTO Table_A(EID)
SELECT 1 FROM Dual UNION ALL
SELECT 2 FROM Dual UNION ALL
SELECT 3 FROM Dual UNION ALL
SELECT 4 FROM Dual;
/
INSERT INTO Table_B(EID,Email)
SELECT 3,'[e-mail]' FROM Dual UNION ALL
SELECT 4,'[e-mail]' FROM Dual;
/
COMMIT;

再看查询：

--有返回记录
SELECT a.EID
FROM Table_A a
LEFT JOIN Table_B b ON a.EID = b.EID;

-- 无返回记录？？？
SELECT a.EID
FROM Table_A a
LEFT JOIN (SELECT EID,EMail FROM Table_B WHERE EID IN (3,4)) b ON a.EID = b.EID;

-- 加一列，又返回记录了!!!
SELECT a.EID,b.Email
FROM Table_A a
LEFT JOIN (SELECT EID,EMail FROM Table_B WHERE EID IN (3,4)) b ON a.EID = b.EID;

-- 用COUNT(*)包一层，结果居然是0
SELECT COUNT(*)
FROM (SELECT a.EID,b.Email
FROM Table_A a
LEFT JOIN (SELECT EID,EMail FROM Table_B WHERE EID IN (3,4)) b ON a.EID = b.EID);

奇怪的是，上面建表时，如果不加主键，则上面第2个查询是有记录的，最后一个也不是返回0.

附ORACLE版本：

Oracle Database 11g Enterprise Edition Release 11.2.0.1.0 - Production
PL/SQL Release 11.2.0.1.0 - Production
CORE 11.2.0.1.0 Production
TNS for 32-bit Windows: Version 11.2.0.1.0 - Production
NLSRTL Version 11.2.0.1.0 - Production

[碧水幽幽泉]

我的数据库也是Oracle11g，使用楼主的语句查询，都是有数据的。

[小灰狼W]

看看执行计划 中间两个语句的执行计划应该是不一样的

[詩和遠方]

真搞不懂，难道底层存储相关，比如表空间或索引什么的